Waterloo class cruisers, in general, didn't carry anything heavier than medium fighters (Rapier IIs, in this case). The Gettysburg carrying Crossbows was an unusual situation, possibly being used because of the ready availability of cruisers, at least compared to carriers, so sparing one for a test platform would be less of a gap in the front lines.
As for the Tarawa-type CVEs, it's specifically noted that they're unable to operate larger ships, which is why they had the 2-seat Sabre bomber variant, in place of the Broadswords carried by regular carriers for bomber duty.