>>36206570It makes sense in a twisted way.
RGBY/GSC were pre-The Pokémon Company. As you can see by the box art of RuSa and on, TPC logo is present.
Regardless of the reason, RGBY/GSC pokémon can't be transferred to RuSa and beyond. Hardware issues aside, the 'mon data are just completely different. And even with the VC workaround, once you boot them to the Bank they're assigned random shit and are no longer "the same" as they were.
Then the RuSa gen and DP gen each had remakes of those old games to bring them up into continuity. You'll then notice remakes skipped a gen and when they came about, so did a whole new alternate dimension.
The GB/GBC games really are off in their own little space. They're relics (don't get me wrong, they are solid games). Just kicking back doing their own thing in limited color and mono sound.