If added buffering logic was added for a multi-pixel write buffer, the jaguar (or CD blitter) would be much faster, likewise, if the CD blitter was at least more like the jag and able to do 8 or 16-bit pixels, it would have been much more useful with the 32x too (or dithered 16 color MD stuff too). Making it more like a general purpose blitter (block copy, fill, etc) would have made it far more flexible in general.
But adding such a phrase buffer would mean more silicon, and possibly something that just couldn't fit into the PGAs being used. (or not in the time span they wanted)
Lots of potential reasons for leaving that out . . . for the jaguar it was obviously cost/complexity for a feature felt to be relatively low priority in 1990/91. (when the Jaguar's core logic documentation was set down and initial chip design began)
And again, I don't think the 3DO or Saturn VDP1 featured phrase buffers either. (3DO would mean buffering 2 16-bit pixels for a 32-bit write to the framebuffer or 2 8-bit pixels for the Saturn)