All C++ compilers have a default language mode, so it would be kind of odd for Clang to be the only one to drop support for it. User expectation is that new language modes don’t break their working code, only introduce new features, so having a default language mode should (in theory) be reasonable. WG21 constantly breaking working code both with new language modes and in older language modes through defect reports shows a bit of a disconnect between the committee and users.