It becomes a legal and business decision for the registrar.
Most serve at the pleasure of a formal contract with their TLD control entity (e.g. ICANN).
Ultimately, if you were to sue them, there's a root document of legal responsibilities and behavior to point to.
In contrast to whatever emphemeral TOS bullshit Google feels like tossing out. And furthermore, unlike Google, they can't really just ignore you.
Or, to put it another way, VISA, American Airlines, Coke, etc also have an interest in maintaining legal ownership of domains. They could care less about Google accounts.