For religious people - because Christianity allows only one spouse.
For non-religious it has a bad reputation due to the way it used to be practiced in the Arab world (and elsewhere) where it’s not symmetrical - a husband is allowed multiple wives but a wife is not allowed multiple husbands.
Lately there has been a rise in acceptance of polyamory - understanding that people may have multiple partners at the same time, and this should be accepted.
TCP and UDP are still possible over layer 2 avian carrier