Time, $ to get started, lack of "intro" opportunity, and politics/personalities.
FWIW I do compete at local and a few regional matches.
If you really want to attract and keep new people, more matches need to host and set beginner-friendly courses of fire and offer equivalent prizes for it that are accessible without pre-registering 3 months in advance, driving excessively, etc. I know every "category" is an additional hassle, but it is possible to make courses challenging while making it so everyone can come and hit enough targets to make them happy, while still separating the top competitors from everyone else. Longer stage times for beginners, stages where a 30-40% hit rate is there if you just want to learn the skills, but it gets proressively harder, etc. Too many times have seen someone start getting into it, but hitting zero's on half the stages, get yelled at by a jersied competitor for going slow or some such nonsense, and if lucky getting called up to a prize table after the winner just got their third scope certificate or pair of binos from a prize table, half the crowd has already left, and now the new guy gets to pick through a pile of leftover stickers, a pink size S tshirt, and a 10% off full retail gift certificate for something they dont even know what it is and can buy cheaper online anyway...well, it doesnt really scream "welcome, we want you here" to a newcomer.
Newcomers arent going to drive 15 hours one way to "check it out", they arent going to buy $3000 in equipment to try something for the first time, most dont enjoy being the only newbie unless they are there with a friend (partner match, hint, hint), and no one really enjoys being an afterthought. I say if the parent organizations want to grow, they need to have some traveling matches that make it accessible within a days drive in all regions, and they need to mandate a good beginner course of fire with an equipment rental option or a true hunting-rifle class, and saving a good selection of prizes for a beginner-class of competitors that lasts longer than 1 match before you get thrown to the open-class wolves. TAC would be a good example to emulate and translate into NRL hunter or similar.