[zeroer]

My guess is that they don't delete anything due to regulatory and legal reasons.

[brokenmachine]

What possible regulatory and legal reasons would there be that they can't delete your account?

It's not like it's financial information.

Any other service (eg Google) expressly says in it's TOS that they may delete your account whenever they feel like it.

[DashRattlesnake]

My guess is they don't delete it because your data is valuable to them and they don't want to lose it, though they may use fake regulatory and legal excuses.