It would be great for this to be reestablished as the norm for online services. I think some might argue that being able to intercept a user at account deletion via support gives them the opportunity to either solve a misunderstanding in the product or better understand why the user is leaving but I think there are much better ways to accomplish this. I’m more convinced this is done as a dark pattern to add friction…
I think it's much more likely that it just takes timeand money to develop how the deletion process works, testing the implementation etc. It's easier to just not have the capability since it's not critical to the majority of users.
And they could still offer an account deletion button which automatically filed a support request. Most sites which don’t offer account deletion have made me dig or google for a solution instead of putting any info in a contextually relevant spot such as in account settings or in a support article about disabling an account.
Unfortunately I do not have evidence to justify this position but for most companies from an incentives standpoint as I understand them: 1) a user who cannot delete an account will have a far easier time using the service again compared to a user who has deleted an account so they are more likely to reengage, 2) user numbers and active user numbers may be important metrics for funding or company evaluation, 3) assuming data is deleted on account deletion then that can no longer be used for marketing or model training, 4) services which rely on the network effects from the user base need to have a relevant and usually large user base to provide consistent value, 5) if done manually there support and or dev cost on each account delete request.