I looked up Troy's 2018 roster the other day and looked at the freshmen and what Brown did with them. I'm going on memory so my numbers could be off some, but it's at least ballpark. Of the 20 freshmen at Troy in 2018, here's what Brown did with them.
14 redshirted, which means they played in 4 games at most.
3 didn't redshirt and played a little
1 didn't redshirt and played a lot
For 2 the website didn't say, which probably means they didn't play.
I doubt Brown had a complete change of philosophy in 2019 and started playing freshmen for the heck of it. I think instead he felt he had no other choice. Given a choice, Brown (and lots of other smart coaches, like Don Nehlen), let the young guys develop while playing the older guys, with exceptions of course for the younger guys that happen to be really good.
Everything else being equal, a player is almost always better at 22 than he is at 18.