Why more HMS Unicorn-type support carriers became light fleet carriers

Why were there not more ships like HMS Unicorn?

There probably would have been, but wartime requirements turned the follow-on need into light fleet carrier construction.

The absence of more direct Unicorn sisters reflected the wartime carrier program rather than rejection of the support-ship idea. Britain still needed mobile maintenance, spare aircraft, and aviation logistics. Wartime urgency favored hulls that could combine those support functions with a useful operational flight deck. The follow-on requirement was therefore absorbed by light fleet carriers instead of producing a line of exact Unicorn sisters.