It takes a lot more courage to flee, a lot less to be a coward and hope they get injured and sent back home. Especially with Russian propaganda telling them the entire time that Ukrainians will torture and kill them for surrendering, that the Russians will torture and murder them if they're caught, and that their family will never be safe if Russia decides to go after them. Plus knowing that if they're captured by Russia or traded back they might be tortured and killed like that Wagner guy the Russians murdered with a sledgehammer.

There's also the logistics of fleeing a unit (or barrier troops) that will kill them for deserting, alone, in unfamiliar territory with a changing battlefield. Having to hope they actually find someone to surrender to without running into other Russians or getting killed from a distance before getting the chance to surrender.

That's not to say there aren't plenty of Russians who just want others to die in their place, but loving Putin and supporting the war absolutely aren't the only reasons people don't desert.