Sure, you can, but if one technology is both "good enough" and "works on everything" I can understand why the developer might only bother with that one. Proprietary, vendor-locked standards leave a bad taste in my mouth.
I would like to at least see XeSS implemented in addition to FSR2, as it's another open standard. With any luck, pressure could be put on Nvidia to make DLSS vendor-agnostic as well, but they've proven over and over again that they really don't care about gamers.