Originally Posted by
lsquare
Which ones?
Airlines whose BE fares exclude a free carry-on

UA is one definite example, but there are probably others.
aside: is there no longer a "share" link for Google Flights?
anyway one random sample, do a one-way search for SFO-LAS on Sep 3rd and select UA in the airline filter. The lowest fare currently is $69 but has the "no bag" symbol next to it. If you click on that it prices out as BE. Go back and click on the bag filter and say 1 carry-on and the lowest fare goes up to $99 in normal Economy.
This won't work for, e.g. DL, where you can still have a carry-on with BE.