I tend to write a lot, so I'm sorry if this turns into an essay
I like things that are different, and this is one of them. He has that goal that many pokemon players have, completing the pokedex. He is a researcher who wants to learn everything he can about pokemon, and catching them is how he wants to do so. That makes sense to me.
Plus, I think it's important to note that he becomes a little obsessed at certain points and it causes him to become negligent of his Pokemon, as well as the fact that he doesn't really battle with them because he thinks using pokeball after pokeball is faster. In the later episodes, you see his and Hibunny's relationship strain, especially in the episode revolving around Hibunny wanting to learn Ember. Goh doesn't see a reason to help his pokemon become stronger, despite the fact that it wants to. That's neglectful. It's almost like, once Hibunny evolves into Rabbifoot, the roles reverse, and Goh recognizes that Rabbifoot is unhappy due to how Goh was behaving as a trainer, so focused on pokedex completion that he didn't think about the feelings of his pokemon. He wants to become a better trainer, and that's important development considering what we've seen from his character so far.
It can be argued that this development could have been done differently, but I think that his wanting to catch every pokemon is a good thing, not so much for his overall goal, but for the development of his character. He's antisocial and self-absorbed to a degree, and has quite the ego; catching so many pokemon and dedicating himself to becoming a better trainer to those he brings with him are gonna be important...I think.
I don't know, I just really like Goh, I'm not the best a phrasing things, and it's 4 in the morning.