1) The anti-alcohol moralists who will do anything to impede access
2) The distributors who want a cut of the action; and
3) The states themselves who want to make sure that they get their tax revenue.
There isn't a lot we can do about the first contingent except to continue efforts to educate people about wine.
The second group is a powerful lobby working out of self-interest. The only ultimate hope to counter them is for there to be a strong enough public interest to outweigh their private one, but it might be that there would be a compromise position in which exceptions could be made for small wineries or limited volumes.
As for the third group, it could be that some of the objections would
go away if the local sales tax got paid. Despite the current suspension
of these taxes on internet sales, it seems that, based on the distributors
I work with, that states are pushing harder and harder to collect the sales
tax for sales into their states regardless of whether one has an office
there or not. This is a bit of a headache to track and file, but the right software can ease this quite a bit.