Pretty much all the factors have been covered here and I agree with most. Expanding on Jared and Jesse's list with 3-gun in mind:
1. Lack of knowledge... up until halfway recently there hasn't been a centralized location for 3-gun. Enos and this forum helps quite a bit but even then it is very overwhelming. You go to Wal-Mart and the beginners guide to 3-gun book is literally the size of an encyclopedia. I elephant dung you not, and that's just an intro, there's no lessons and tactics covered. And, unless you live in a big city with access to these things, it isn't like you're going to have a bunch of buddies who are in to 3-gun. I'm trying to get into it but I feel pretty isolated and even to this day all my buddies think I'm a weirdo for embracing this sport. It's hard to figure elephant dung out in this situation. I mean, for example, literally the closest person I'm aware of that has a Glock trigger job that I could potentially try lives 4 hours away. Just kind of hard when if you want to see if something works you just have to buy it then see if it does work.
2. Scared of competing... just look at random 3-gun videos on youtube sometime. You will see Jesse here, Clint Upchurch, Taran, Pat Kelley, Lena/Jerry, Daniel Horner, and otherwise a whole army of people who can make you think WHOA, hang on a minute, what the hell am I doing, I'm going to spend thousands in equipment then hundreds of dollars for a match just to get laughed at! Personally I think the popularization of the club scene helps a ton with this, you'll find that there's a bunch of dudes just like you just trying to have fun and shoot their guns. No big friggin deal. Until you see that there will always be a huge intimidation factor due to massive misconceptions. I think the proliferation of these misconceptions are the biggest problem. Golf was mentioned which is a good analogy... until you get past the misconceptions you literally think that it's on the same level as thinking you can hold your own in golf against Tiger Woods. I for one wouldn't even attempt to do so and would never expect that Tiger would appreciate me being on the course the same time as him.
3. Expense... it's not just local match expenses like Jesse mentioned. That's cheap. Hell I can't even find anything 2 hours away. When you're not sponsored and don't reload and you're looking at 50 cents a shot and a minimum of a couple hundred rounds, thousands of dollars of equipment, a minimum of 3+ hours of driving each way, a night or two or three in a hotel, meals away from home, I mean that crap really adds up. If I didn't have my own side business in addition to my day job, I could never even think about doing any of it.
4. Time... If you really could just spend one day and leave early afternoon that wouldn't be bad but that's best case scenario. You can easily not just burn up the whole weekend but have to take 2-3 days vacation for these bigger meets. Hard to justify here in this country where most people don't exactly get 3 months vacation if you have a family that is competing for your time. It's easy to say to bring the significant other along with you, but that's not really realistic with a wife and 3 kids.
... adding my own reasons...
5. Simple interest... I mean, 3 gun is cool. But why would I burn up an entire day shooting at bowling pins or plates from a stationary bay? Silhouettes? Trap? Yeah right. Boring. I'm sorry. I have better things to do. I'm sure there are people out there wondering why folks like me don't get big into trap and try to blame it on me being scared or whatever... it's just friggin boring! The bird flies away from you. Over and over. Combat plates? You set them up and knock them down. Over and over. I have better things to do.
6. Social skills... matches are basically 90% talky talky, and 10% actual gun stuff. I'm not so good at talky talky, and until I just jumped in and figured out that there's a bunch of guys like me that I can get along with, quite honestly the social anxiety factor was much more intimidating than the gun part. You see the alpha male types hanging around and expect it to be on the level of walking into a jock based fraternity that you aren't a member of and never will be. Sad but true.
7. Age differences... 3-gun is becoming popular because it brings the young guys who like adrenaline out. Without that venue, you've got things like skeet and 600 yard rifle, which is primarily older gentlemen. It's been hard for me to visualize spending a whole bunch of time with the local crowd that I know are into other shooting competitions due to the age gap and the things that come along with that.
Jesse Tischauser said:
1. Lack of Knowledge - Either they don't even know it exists or they have heard about it but don't know anyone that does it and can help them feel comfortable about giving it a try
2. Scared of "competing" - Most think its a real competition. It's not in the sense that everyone will be watching and judging your performance like my gymnastics league. I liken it to golf. If there are 4-5 guys at any one time actually paying attention to you while you shoot you're lucky.
3. Expense - Ammo ain't cheap! I used to balk at a $50 round of golf and a $5 golf ball I might lose. Now I will drive 2 hours each way, pay $10-15 to play, and shoot up $40-80 in ammo 2 or more times a weekend if I can find a match.
4. Time/convenience - Shooting matches is a huge time waster. Get to range at 9:30 leave at 2:30-3:30 for 5-7 stages and 2 minutes of actual shooting. I'd still love to see someone try to setup a 5-7 stage club match or steel challenge like a golf course. Once your certified to shoot unsupervised ie you take RO course or something similar you can show up anytime to the range any day of the week pay your $30-40 (like a green fee) and shoot the match. Turn in your scores and they go up on the online weekly match scores. I think it could make a viable business as I'd go shoot evey night of the week and I know I could talk others into going. My old oilfield buddy's do a lot of golfing and clay shooting during office hours to entertain clients and themselves. This would be right up their alley too. Like golf or sporting clays or that cool indoor golf carting track in OKC.