See, there's the rub - you aren't looking in the right direction. I see pictures of winter hammock setups all the time - over on hammockforums, where hammockers congregate. You're not talking apples and apples - hammockers can and do winter camp if they choose to and enjoy it. Winter campers who prefer tents, use those instead. There are plenty of advantages to both - that you don't see them all doesn't mean they don't exist. Your reasons are your reasons and no one else's. Flat statements about any sort of backpacking gear being inadequate or deficient don't fly. People are defying your expectations every winter. If you don't believe posters here, go to youtube and google Shug's videos. He's testing tarps, stoves, and hammocks in his backyard on a regular basis, in 17F and below.

Me, I camp in 4 seasons, and use a hammock all the time, regardless of where I go. I don't do snow or arctic weather; I go somewhere else, ie the coast, where it is usually freezing at night but no snow. But that's my choice, and I do very well with it. Being lighter is not the point of hammock camping. Being able to walk the next day is the point of MINE.

I'm not going to convince anyone to use a hammock - I don't care if you sleep in a tent, hammock, bivy, or a 55 gallon drum. Go for it. I'm just making the point that your belief that there are "too many reasons not to use a hammock in winter" is entirely subjective, and there are lots of people out there merrily proving you wrong - clearly their "reasons" are different.