My honest guess is that there is a little sleight of hand here. Yes, WotC has said humanoids do not have a set alignment, but WotC has not ruled out alignment tendencies for things that aren't humanoids, and they have turned a lot of humanoids that traditionally were antagonists into non-humanoids so they can keep their alignment tendencies. Monsters of the Multiverse pretty much explained this in a little sidebar on hobgoblins of all things (stating PC hobgoblins are humanoids and have a variety of outlooks, while the monster hobgoblins are fey and influenced by fey magic, so they can have an alignment).
This has several ramifications. First, it lets WotC keep alignment on a lot of creatures that otherwise would end up in the "no specific alignment" bin. Gnolls can remain mostly evil, githzerai mostly chaotic, etc. It also tries to keep the classic play style alive while also addressing the concerns of biodeterminism. However, I think it's a compromise that ends up upsetting both sides. Most bio-essentialism proponents aren't satisfied that "they aren't humanoids" justifies goblins and gnolls having evil alignments, and those who rejected the concept see them unnecessarily messing with monster types. And, of course, it will raise questions regarding the PC versions of these creatures remaining humanoids and weakening X Person spells.
But yes, this is WotC trying to have its cake and eat it too.