#1) They can't confiscate firearms passively. Most of the left imposes their tyranny at arm's length, remotely from Silicon Valley, state capitols, and DC. Someone has to come and get the firearms from the populace. #2) It's much easier to resist passively. Rather than having to donate, show up and protest, vote, evade taxes, etc. all that must be done to rebel is not to comply. And nobody likes being stolen from.