>>29605084Digimon is a different case.
They are, first and foremost, a bunch of data. Like, literally, they are data in-universe.
Much like any kind of data, they can be compressed and decompressed, which in turns changes their size.
I mean, hell, in the first Digimon movie, we have kaiju-level Parrotmon and Greymon.
Pokemon are real life being in-universe, so them being manlet (at least, for those who logically shouldn't be) is noticeably jarring.
Source:
Headcanon 