The complaint that everyone makes about the "lack of Johto pokemon" only makes sense from a modern perspective where the draw of each game is all the new Pokemon out there. Gold and Silver were not constructed as "another entry in the series" they were designed to be a sequel. The Johto mons are an expansion to the roster, not a replacement for the original dex. Why are some of them locked to late or postgame?
a) They add variety to the world, and they help make people's experience unique, and some people like to swap out members of their team throughout, they don't settle on six early and minmax them
b) kids who play pokemon often don't just go through the story and put the game down. They spend hours fucking around with all the extra features, playing around with their team so they can meet up with their friends and show off the rare Pokemon they caught, or try out new setups to battle each other. This kind of approach might be dead now, but it wasn't for kids in the 90s.

The draw of gen 2 was partly an EXPANSION of the original dex, but mostly it was the new world, it was the new features, have you tried playing Red and Blue lately? It's a slog and everything feels so antiquated. Crystal on the other hand is still a blast even with the incredible remakes existing alongside it, it adds so much to the gameplay, the environment, everything is more fleshed out. Because the Nu games don't have any of these things all you expect is "OMG THEY MADE A NEW BUIZEL AND NOW HE HAS A FUNNY HAT AND MOUSTACHE" rather than any actual improvements in gameplay or interesting new features.