I wouldnt call it gate keeping, everyone can express their wishes and it makes sense that for animals similar between america and europe the NA playerbase would prefer theirs, they are simply a bit louder about it, meanwhile european players are mostly just on the defensive to want their animals.
To put it simply, either both are equally boring or none is, but most people seem to appreciate the wild North america more then the european one, which i honestly wouldnt even care about if the anti europe haters wouldnt be so annoying at times.
I think it is for two reasons:
1. The first year and half of support wasn't particularly kind with Europeans in term of animals, so each animals we were receiving from our continent were already a big deal for us and mostly presented as NA or generic species (e.g wolf, reindeer or flamingo) (I would have never we would have two packs more or less dedicated to us, despite knowing that we were having a way higher diversity than what people want to admit). Personally, I enjoyed a lot of NA animals and in particular the ones that we find in Europe or with equivalent species (beaver, grizzly).
2. A part of the community from NA, probably the smaller amount but the noisy and the most trolling part, was constantly neglecting and lowering the interest of EU animals (I remember hearing and reading that EU wasn't worthy of a pack and would never have) and after that freely criticizing and lowering the EU pack. If there is this equivalent in the EU community it is for sure way less noisy and visible (smaller amount ?).