Developer time is spent once. Users will always have to pay the price of additional run time. For. Each. Single. User. Always.
It scales!
Due to the scale of, e.g. slow front-ends, with millions of users, this takes a HUGE amount of time. Only to save a few hours or days to develop it better.
Having 1 million users each wait a single second is already 11 days. If they have to wait that single second for each interaction, it quickly adds up.
It is also bad for the environment due to scaled up inefficiency and resulting increase of power usage.