Most applications clog up the cache space on your device’s memory. You have to delete the cache manually which is not convenient. Fedilab is one of the few applications that has a self-cleaning cache function when exiting the application. Why don’t many other apps have a feature to disable caching or self-clear the cache?
Most things like this come down to resources. You have a finite amount of development resources and this is likely way down the list of features. Especially as there’s already a button to do it manually.
All features have to be planned, designed, implemented, tested and released. None of those steps are free.
Chances are the development resources are being spent elsewhere on more important features.