Just because a lot of people are using them does not necessarily mean they are actually valuable. You're claim assumes that people are acting rationally regarding them. But that's an erroneous assumption to make.

People are falling in "love" with them. Asking them for advice about mental health. Treating them like they are some kind of all-knowing oracle (or even having any intelligence whatsoever), when in reality they know nothing and cannot reason at all.

Ultimately they are immensely effective at creating a feedback loop that preys on human psychology and reinforces a dependency on it. It's a bit like addiction in that way.