In the context of almost every proposed causality violation mechanism I've seen seriously discussed, it really is can't, not won't. Wormholes aren't the only example. Tipler Cylinders for example don't allow time travel prior to the point when they started rotating. Godel's rotating universe has similar restrictions. Is there some time travel proposal I'm missing?
I agree that when considering anthropic issues won't becomes potentially relevant if we had any idea that time travel could potentially allow travel prior to the existence of the device in question. In that case, I'd actually argue in the other direction: if such machines could exist, I'd expect to see massive signs of such interference in the past.
In the context of almost every proposed causality violation mechanism I've seen seriously discussed, it really is can't, not won't.
There are plenty of mechanisms in which can't applies. There are others which don't have that limitation. I don't even want to touch what qualifies as 'seriously discussed'. I'm really not up to date with which kinds of time travel are high status.
http://www.nature.com/news/2011/110922/full/news.2011.554.html
http://arxiv.org/abs/1109.4897v1
http://usersguidetotheuniverse.com/?p=2169
http://news.ycombinator.com/item?id=3027056
Perhaps the end of the era of the light cone and beginning of the era of the neutrino cone? I'd be curious to see your probability estimates for whether this theory pans out. Or other crackpot hypotheses to explain the results.