Sidechain and other L2 already exist far before Ordinals created. But almost no one use it despite both Liquid network and Rootstock have smart contract capability and developer behind it promote it support NFT/token. I also have seen Ordinals supporters say they only want to use Ordinals since their arbitrary data guaranteed to be immutable.
I think I adequately explained why the NFT bullshit doesn't use alternatives (I mean forget sidechains, they could just spin up another blockchain or use bcash or whatever). If it wasn't clear you can ask questions.
Of course, there is also always the potential for collateral motivations but if you pick through them the most likely sound like ones trying to divide up the Bitcoin community, or trying to prove out points of control or that transaction censorship works. ... but you don't need alternative motivations to explain the shitcoining, it's just that even when one is sufficient others can be true too.