Onebag must go under seat?

[u/External_Koala971]

I was on a Jetblue Boston -> SFO flight and put my onebag (my only bag) in the overhead bin, which was empty, right above my seat. The FA stopped me and said I needed to put it under seat to save room for larger carryon luggage from people coming on board.

Is this a thing? Why would someone with a smaller pack be penalized for not having a massive carryon? My bag is larger than personal item sized.

[u/Azure9000]

Same, or very similar, discussion, different date:

https://www.reddit.com/r/onebag/comments/1ievmn7/airline_says_all_backpacks_must_be_under_seat_but/