Amputees can absolutely accomplish a lot and live fulfilling lives. But it is a disability at the end of the day. No professional military would allow amputees into combat arms unless their recruiting pool was in danger of collapse. Which, after almost 3 years of war, it likely is, for both sides.

There’s a long history of doing just that, both for reasons of experience retention and because recruitment is almost never flooded with quality recruits, beyond the occasional initial outburst of enthusiasm. Recruitment doesn’t need to be anywhere near collapse, for either side.

The reason why we aren’t used to it is because most of the wars we’re culturally familiar with in the past ~90 years have been reliant on power projection, wherein the fighting capacity of every individual must be maximized relative to their logistical footprint - when you can only send 50 men to a position in the next 24 hours, you send the top 50 you can get. Furthermore, many of the wars Americans are familiar with in the past ~75 years have been heavily reliant on maintaining good PR and low allied casualties - injured troops going back into combat are a bad look for a cause that might already not be wildly popular. “We are winning easily with no problems” is the narrative that must be peddled there for an unpopular cause - for Ukraine, it is “We are fighting for our existence”, so that particular PR point is less important.

Ukraine is fighting on its home turf, and Russia is fighting on its own border - sustaining an amputee at home or at the front have similar costs, but dissimilar benefits for veteran volunteers. There’s no Atlantic or Pacific Ocean between home and the front to make getting a man or his needs from point A to point B prohibitively expensive.