But it's clear, even outside of forfeiture, that that isn't a requirement for losing property to the state for wrongful conduct; civil process (with the government having a cause of action) does exist even outside of forfeiture, even for conduct which also has criminal punishment.
There has never been a principal accepted in this country that all government legal remedies against individuals require criminal conviction, which is what you seem to be asserting ad the principal with forfeiture.
It's clear that certain types of penalties require criminal conviction, and it's clear (now at least, though that should have been obvious before) that penalties expressly premised on criminal conviction require criminal conviction. But forfeiture doesn't really fall into either of those categories.