Gate checks are part and parcel of flying today an all airlines at least in Europe. Passengers can (attempt) to take a damn lot of stuff onboard.

It's probably a majority of my flights that staff looks for bags to be gatechecked and indeed status pax are usually left with their carryons unless volunteering.

Putting it on a light-fare having non-FF BP makes sense. They are both more likely to have an oversize bag as well as less likely to know that this is a thing that happens (plus being "first in line" for an involuntary gate check)