This is a very deep question you are asking and can't hardly be explained in messages on this forum but I have been a part of the rise and recent fall of tournament paintball for around 17 years now. The most obvious answer is money! It is very expensive for players to play every weekend to get to a level were they can consistently compete in tournaments and be successful. Since there are basically no contracts in paintball especially at the d5-d3 level If your team is not successful then players jump ship very quickly to a team with better deals. And typically when good players join other teams the remaining team crumbles. Successful teams typically have a high turn over (players quit, go to college,start family's). So these teams are always looking for new talent (gobbling up the best local prospects).
Back in the day there were many fields all with at least one home team sometimes more. Tournaments were plenty full and everyone had a lot of fun trying to become the best local team. And there was prize payouts that actually made the tournament worth playing in. Back then owners of fields saw value in having a team (probably played on the team themselves or kids my have). Most of those fields have now closed. Now the fields that have survived have only done so by the money they make off of the rental game. And do not see the value in tournament paintball.
Des Moines has made it nearly impossible to open new fields, especially in city limits and with our population growing so well every year in and around Des Moines developers have made land prices skyrocket making it a very large investment to open a new field that is capable of providing new opportunities for tournament players. Also most people around these parts wouldn't even have the power, knowledge and ability to provide this and the ones that could don't have the money to make it happen.
In closing paintball is expensive and how the PSP was handling there business for the last 6 years (charging crazy money for teams to win entry fees). It didn't give people much of an end game, they became the best local team, then a Midwest power house, only to spend all their money at national events and get nothing in return (now the teams have no money and are reranked so high they can no longer play lower events). It burned out 100's of people I used to know
now we have the NXL maybe if they handle their business currently it will give people something to believe in again and the players might start coming back!! We will see
If you would like much more detailed answers to any questions you may have I'm always willing to talk about how tournament paintball ruined my life
Hope this helps