You are right. After reading this I requested Uber to delete my account as i was using a prepaid phone while visiting the US. I was very disappointing as they don't have an easy way to delete an account, you need to send an email explaining why.
What I'm saying is that while I do find it mildly annoying that there is no "Delete Account" button there are good reasons for it. Not is this a non-insignificant amount of work to build/maintain but from a business point of view it means spending time/money on a feature that is only for people who no longer want to be your customer so put in that light it's no surprise this feature falls by the wayside often. Also there is the whole "I accidentally deleted my account" (no matter how many warning you put up) and that means you either need to "soft delete" all the data so you can "undo" OR you have to reconstruct the user's data from a backup (either programmatically or by hand).