You mean the sudden change of useful headphone base prices from sub-ten-bucks to whatever it costs for even cheap BT headsets?

Yeah, almost certainly.

It's a common and likely hypothesis, yes.

Although I feel like these days I'm more likely to run into people taking video calls on speakerphone in public than blasting their music.

I want the parallel universe where phones kept the headphone jack and it was the cameras getting pushed out into dongles/BT.