You mean lock it within settings after it gets stolen while it's in the cyber-criminals hands? I do not think that's a viable solution. All they have to do is take it, point it at you and run away.
Again, if we focus away from government/police, cyber-criminals have a less intrusive and physical way of getting into the device. Moreover, by the time a user gets another phone/gets home, requests the phone gets remotely locked, the cyber-criminal would have already breached your confidentiality/privacy. If session ID cookies are used (which they likely will be), the cyber-criminal can steal a large amount of data, without needing to do an otherwise sophisticated attack like XSS/XSSI/CSRF.
Previously mentioned, for those that are computer-novices, this point has further strength.
Edit - Cut it down in case it is thought to be a of a political nature, even with the disclaimer and no off-content/political references, I'd rather be on the less risky side