In ZA specifically, I'm fairly certain they've mentioned more and more wild Pokemon have been showing up, it's like a plot point. A lot can happen in 5 years when Pokemon seem to proliferate relatively quickly.
>>723591554 (OP)
After the great pokewar, most of the planets population is decimated, and regions are closed off from one another, starting at r/b/y. Those games also mark when humanity finally started to rapidly rebuild and reconnect again, and every region shares their knowledge and helps migrate domesticated pokes all around.
>>723591554 (OP)
Apart from gen 2 when they were initially said to be newly discovered pokemon, there isn't one. They just don't happen to appear. quasi-exception for cameos like munchlax being in pokemon dash before gen 4 released
>>723591713
For all its faults, ZA gives a concrete reason why all these new mobs are showing up, it also says the new metas are only recently discovered