Dreamstime and 123rf offer a TIFF as well - same as SS, created from a JPEG we upload.
I think the idea when they introduced this was to give the old-school macro agency customers what they were used to getting (upsized TIFFs) rather than arguing with them that the JPEG from the camera at native size was just as good.
Getting a 16 bit TIFF created from the RAW or PSD file would have some real value, but probably not enough and for too few customers to make it worth the hassle of dealing with other formats.
Pond 5 has just announced they're accepting PSDs; I sell a few PSDs at Creative Market. There perhaps will emerge more places where files other than JPEG can be sold.
At DT and 123rf I've sold TIFF files; always amazes me, but the sales do happen