Ash has made it VERY clear in multiple regions, over 20 years now in fact, that he has a goal besides adventuring for the sake of it, that he desires to become the World's Greatest Pok?mon Master. And DP made it very clear that becoming Champion Master is, if not the endgoal, then certainly a step in the right direction.
If they really wanted Ash to just have adventures with his friends and making Pok?mon captures for the sake of it with no goal in sight besides that as you seem to be implying, they would have depicted Ash the
same way they depict Sonic in the end of Sonic Heroes.
To put it another way: Think of it like Punch-Out, or the Rocky movies. Those stories have a definite end-goal, and Ash needs to win the league and beat the Elite 4 to actually achieve his goal.