Some of SSE is required as part of the x86_64 ABI, and also new versions of Windows (infamously, now) add required CPU extensions so software will often base it

Some of SSE is required as part of the x86_64 ABI, and also new versions of Windows (infamously, now) add required CPU extensions so software will often base its requirements on that. And SSE4x is ubiquitous enough (99% of PCs) that some software/games will just require it and simply crash if it can't use those instructions.