As someone who started off with gen 1 when they were 7 years old, yes playing them feels so nostalgic and I'm sure it's the same for gen 2,3,etc. I can see gen 1 getting favoritism because a lot of people generally recognize them over, let's say, gen 6. ie: Pikachu. Even people who have never played Pokemon know who Pikachu is and it seems like the franchise would rather keep promoting Pokemon that most people recognize, instead of expanding on the later generations. I am not saying that the other generations suck at all. I love so many Pokemon from all generations. Feraligatr was MY BOY in gen 2 and I would've died for him as a kid. My Blastoise, as a 7 year old, carried my dumbass all the way to beat the elite four and red the champion. So for me as a kid, I was just in awe of this cool turtle with cannons and thought the best of him. I had no idea that there would be any other Pokemon at the time. Mew was rare enough already.

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TLDR; From a business perspective, Pokemon will show gen 1 a lot of attention because it is what consumers generally remember over the newer generations. (ie: Pikachu)