California constitutional amendments are not really constitutional amendments in traditional sense, just a way to pass legislation by popular referendum. In theory requiring supermajority for referenda would be a source of a massive status quo bias, what would be extremely undemocratic.

California has a system for passing legislation by popular referendum. At least in the case of Prop 8, the use of the amendment process instead was to bypass challenges to the legislation's constitutionality. If we required a supermajority for amendments, but not ordinary referendums, it could stop the abuse of the amendment process to pass what should be ordinary legislation, subject to constitutional limitations.