Why do you assume it is the wife that wants to stop?
Probably because she is married to a normal healthy man and knows other normal healthy married men. Now, sure, there are exceptional saints and very holy couples who after a great deal of discernment, prudent thought and spiritual direction might take this step. But dollars to donuts none of them are hanging around on Internet forums looking for advice or dishing it out. I bet they also are VERY discreet about it because of their prudent concern that some people might misinterpret it as a slight on their own marriage or that post menopausal sex was "lustful"
If some rare couple are contemplating making this sacrifice in the right spirit (and not because of latent ɧoɱosɛҳųαƖity or a unbalanced disgust of a natural act in its proper setting, then they are busy with praying, good works, assisting a masses, sewing scapulars, fostering children and a hundred other things. Any priest guiding them would make sure that this was an appropriate sacrifice for a very spiritually mature and saintly couple. Plenty can go disastrously wrong otherwise.
My guess is that a lot of the people promoting sexless marriages are not even married. Aesop was warning his readers about people like that 3000 years ago.