That does make sense from a historical perspective and I don't doubt that's why. But still I find it unsatisfying because any competent database schema will always retain the history that needs to be retained. If you don't have the storage capacity, you choose to not store so much history. If you don't have native concepts for storing history, you kludge it yourself.
Whether you have native temporal support or have to kludge a DIY solution in the schema, the data you need to store gets stored.
My frustration is that I feel that temporal concepts should have been deeply native to SQL right to its core. History should have been as fundamental to database design as columns and rows. It should be a thing you turn off when you don't want it, not a thing you turn on when you do.