>>537725008
They're just small carriers with 50-70% the complement of planes as fleet carriers. Battleship-sized hulls are too big for most shipbuilders, so if you were okay with something cruiser-sized you could get a lot more of them built at once.

Escort carriers were usually a little smaller than that, but they were also slow as balls. Almost 20 knots, vs. just above 30 for light or fleet carriers. That was fine for convoy escort duty.