Humans have emotions and don't think rationally by default. Most people do not like to feel inadequate, though how they respond to that feeling varies a great deal. Most people in a relationship also don't like to feel they were rejected sexually over some perceived inadequacy.

So when a mate gives them a 20-page lecture on their failures to hold their attraction and concludes by rejecting them as a sex partner, it's probably not vanishingly far from the null hypothesis that the person is going to get upset...