Alternatively, we could strive for a system than doesn't put women in the situation of having to stay married in order to survive. Just throwing it out there.

You're right on one count, though: finding a better man may not be easy. They're a limited resource, and most of the best ones stay married. If one does come on the market, there's the reality than he'll be choosing from a large pool - a 45 year old man will have options not just his own age, but in their 20s and 30s. The competition will be steep.