Are you operating at scale? I hope you have a very robust backup system (including enough that you can even recover from something like the Sony hack), and so you're going to need to ensure that you delete it from those systems. And then, you're dealing with 100s (1000s? 10000s?) of these deletions a day. Do you want that to be instant? Are you really that confident in your deletion that you want it instantly overwriting your backups? How are you resistant to the Sony hack in that case? ...
I don’t know about a general purpose system for this, but it’s generally easier to proactively delete or make inaccessible something in a singe data store. Encryption reduces the problem to a single element in a single data store. You’re not wrong, but it’s a problem worth solving for the ability to not have to solve the problem 1000 times over for each bit of user data.
Are you operating at scale? I hope you have a very robust backup system (including enough that you can even recover from something like the Sony hack), and so you're going to need to ensure that you delete it from those systems. And then, you're dealing with 100s (1000s? 10000s?) of these deletions a day. Do you want that to be instant? Are you really that confident in your deletion that you want it instantly overwriting your backups? How are you resistant to the Sony hack in that case? ...