I think it had something to do with the anime for me. As a kid I watched the anime that followed the first and second gens so I was committed to each and every Pokemon. When the third gen came out, I wasn't watching anymore so it was just a bunch of new things that I had no story connection to. Also my first game was Silver, and I backplayed through the first gen games, so I have a bit of first game nostalgia for Gen 1 and Gen 2 as well.