The key distinction is between punishing you by taking property that is yours (criminal penalty) and taking property that is not yours in the first place (civil forfeiture). In a civil context, preponderance of the evidence is the typical standard. E.g. If I sue you for embezzling my money, I don't have to prove beyond a reasonable doubt in order to get my money back.

I think civil forfeiture has major problems with how it's applied, but it's pretty internally consistent with the rest of the law.

There are at least two major difference between civil asset forfeiture and civil litigation. First, the plaintiff is the government, and the government has vastly more powers and resources than typical plaintiffs, making it more difficult for ordinary people to defend against them and more reasonable to demand from them a higher standard of proof. Second, in typical civil litigation, the plaintiffs don't seize your house/car/money first and put the burden on you to initiate litigation to get it all back now that you no longer have any resources with which to fight that battle.