

Likely bad coding or bad database design.
Best practice is to avoid using email as primary key in the user database, instead use an internal ID, so that an email change can happen without touching the primary key.
Your reply made me think of an alternative to deleting accounts : replace personal information to use a pseudonym and a throwaway email, remove everything that can be removed.
That would help once the badly coded website get hacked or its database get leaked.
Then why doesn’t it adjust to avoid negative social and environmental effects? Probalby because it’s not possible to adjust bitcoin’s algorithm, only some parameters, and because miners don’t have enough intensive to abandon bitcoin for something less destructive.
My understanding is it’s not possible to modify nor fix bitcoin’s core algorithm, which include the difficulty and consensus logic.
A hard fork is possible, which means leaving the bitcoin network and setting up an alternative (hopefully better) network with a different algorithm.