In practice it's very difficult to prove you didn't. So even if she lost her job for unrelated causes or simply quit against your wishes, juries tend to concede alimony unless you make disproportionate efforts to produce proof.

You also pay off she says, "I don't want to work." Considering that it's illegal (as it should be) to force your spouse to work (or stay at home), your point is irrelevant.

It is relevant, because in majority of marriages in USA both partners work. Stay at home women, especially stay at home women without small child at home are minority among married women.

You all make it sound as if stay at home women was the norm, but it is not the case.