Except with a VPN you’re not identified by the servers you connect to, so they can safely not log any traffic and as such, law enforcement can’t ask to hand out data about a specific account because they don’t know which account did it. Same goes for logging the IP of the account, because again, they don’t know which account it is, and can’t force a service to log all users for the sake of finding one.
VPN and Tor and I guess i2p can disguise your IP address indeed.
It’s not true for mail services however, as the email address is your login and/or is linked to a specific account, forever and exclusively.