My son is starting 1st grade this fall, has been at same school since he was 3 and it goes through high school so, these are and will be his peers and it starts as major FOMO/it's the main way kids socialize outside of school hours. Good way to burn off their energies, etc. But it's also, they're young, we want to expose them to everything, they can find their "thing", etc. He does tons of non-Athletic stuff too (STEM, art, music, etc). So we've been playing soccer, baseball, flag football, basketball, lacrosse, swimming, etc. the last few years. It's getting to the point where some kids dropped a few sports based on disinterest or parent's inability to keep the schedule. We have one kid so really no excuses for us, but some people with multiple kids doing this is a scheduling nightmare. Anyways, what's already started to happen is we've brought in hired coaches. In no time, they'll be club/select league aged and people will faction off to do that. When it does, it will feel like gravity/inertia to do the same. Once you do, if you skip a beat, your kid is basically giving up the sport. They can't just join the baseball team in middle school, they won't make the cut against kids that have been playing non-stop since they were <6.
It is their entire friend group and becomes their identity. It would be hard to intentionally tell my son "you're not playing sports anymore". He may come to that conclusion on his own or coaches may cut him at some point; that's life. But, for those that stay active in it, the inertia of it is strong.