How willing would Russia be to admit they deserted instead of surrendering or capture? Each family you punish is like telling their every colleague, relative, neighbor, and friend your army is faltering.

Why not allow the families of deserters to immigrate into Ukraine as well?

Though if invasion failing is what finally takes down Putin's regime, then the deserters might likely be granted pardons by the next regime.

If they are still alive.

Wait, we're talking about deserters who would have opted to take political asylum in Europe instead of fighting. Why would they be dead?

There are a few steps between sneaking away from your unit and securing political asylum in Europe.

Do you sneak away at the front? The opposition is hunting infiltrators, will they ask questions or shoot first? Do you sneak out behind the front? Your own side is likely to dispense quick "justice" and report you as KIA if you're caught (less trouble). How do you get to a border with a Western country? Do you stay in Ukraine and wait for things to settle down before making your move? That's a bet that you won't find yourself in a Russian-occupied zone. And so on.

Novichok