So basically every email provider, Google, and most of the internet has absolutely no user obligations? That's simply not true, even a cursory understanding of contract law would tell you that. Compensation does not have to be currency to form a valid contract with obligations.
They might be obligated to give notice and let you get your data out, but Google could absolutely remove features from GMail at its discretion. Providing a service doesn't make it obligated to continue providing that service forever.
Google's ToS (which you've agreed to) pretty clearly gives them this authority.
They have a contractual obligation to abide by their Terms of Service (that you sign when you sign up for Gmail) or notify you of changes to them. Not paying currency does not make a contract invalid. The fact that those ToS are broad and easy to amend doesn't remove the fact that there is a contractual obligation.
