It is not that uncommon for people to experience severe dementia and become extremely needy and rapidly lose many (or all) of the traits that people liked about them. Usually, people don’t stop being loved just because they spend their days hurling obscenities at people, failing to preserve their own hygiene, and expressing zero affection.
I would guess that most parents do actually love their children unconditionally, and probably the majority of spouses unconditionally love their partners.
(Persistent identity is a central factor in how people relate to each other, so one can’t really say that “it is only conditions that separate me from the worms.”)
The United States is an outlier in divorce statistics. In most places, the rate is nowhere near that high.