There was a time when bdsm sessioning was not a luxury cost option, and it was realistic for an ordinary chap to sign up for multiple hours. Even then, when coming to the edge of one's endurance in a session, it was a thrill to be taken 1 step further because the Lady just "had to" get Her way.
I started sessioning in about 1979, and I never heard of safewords until the 1990s, and I mostly heard of them from Dominatrix professionals who chose not to employ them.