It seems like high level travel participation has gone up but from a local perspective from someone who has been in the same Little League/School system for the last 19 years here is what I've seen:
2016 grad - had about 20-25 more kids in the little league program when he first started and lots of kids who could really play. We had a full LL season of 18 games and playoffs, a travel season of 18 games where we had to really cut players to get down to 14 (which was too many) and had a good competitive local travel team for his 9u-11u years (he also played in a more competitive league on Sundays and went to Cooperstown with that team). By his 12u team those numbers started to dwindle. We struggled to get 12 kids to just play 12u travel - no need for cuts. We had a kid visiting his grandparents from CA for the summer who was previously from our town. He kept showing up to watch - he eventually ended up catching half our games. That year we cut one of our teams because of numbers and re-drafted those kids into the league.
His 12u LL season he tried out for our modified middle school team (7/8th graders) - 98 kids tried out.
2020 grad (my 9th grader) - 25 less kids in the LL. We had travel for his age group for the summer and struggled to get 10u players (we got 12 by pulling up some 9u players who were in his grade). We were horrible - 10 of those 12 kids dropped out the following year because their traveling lacrosse team coach told them they could not do both (they since changed that stance). We did not field a travel program for that age group his 11/12u seasons - he played somewhere else his 12u year.
His modified tryouts - 35 kids.
Last year the HS dropped the freshman program (it was the only sport with a freshman team because the demand had been so high). Less than 10 kids showed up for tryouts and they had not planned on moving kids up from modified (plus budget concerns).
I'm on the board of the LL - we've done a ton to try to make the game more fun (events, food, raffles, give aways), we've sponsored some kids who may have not have been able to afford it, we've worked entire seasons around the local lax program (to have games on alternate nights for Lax practice), we have the HS coach and varsity run a clinic for the LL and minor league programs - and we still struggle filling out the teams.
Both programs in our closest neighboring towns report the same issue - we've had discussions with one to combine leagues but we haven't pulled the trigger yet.