It's an easy game I can relax to. Yes, it's nice to challenge yourself with a game from time to time, but every now and then, you wanna kick back and relax while playing a game. And to date, there's only four series that do that for me, with Pokémon being the oldest of that bunch for me, though it was soon followed by Harvest Moon, then eventually Animal Crossing and finally Minecraft.
Pokémon was also the first of that bunch that was portable, and I've always loved my portable systems.
Plus, if I really want to, especially now-a-days, there's a large number of these things to catch, and I can easily try to be a completionist in this series without pulling my hair out.
And since I don't give a crap what others think, I can still play it now-a-days despite how "old" I am and how "kiddie" the series is. They can just shove it.
--- The best laid plans don't last a second in real life. In the end, all you can do is bum-rush your objective and hope for the best.