>>33381416We can come up with scenarios but for one thing. SM/Alola is like a vacation to Ash after having to stress about winning leagues for the past few regions. In the end of BW, Ash was telling himself that this time he would win the league when he enters Kalos which might have been that start to his change in attitude. And in the end of Kalos Ash just wanted to relax and enjoy himself like a regular kid.
Ash is not stressing about leagues now and he's just having fun training in Alola to do trials. We do see his serious sides every now and then but that's during actual plot episodes with Lillie/trials etc.
