It's actually because RN philosophy was until recently to be able to hangar all aircraft, which when they were designed were Fireflies, Sea Furies and so on. Just before aircraft began to grow significantly, not least in height.
The hangar height in that class was about the most that could be included and meet stability requirements, given infrastructure limits on beam.
QEC is the first RN carrier designed with hangar capacity below designed aircraft complement. There is simply not enough volume in any hull to get all aircraft hangared these days