By the time git became well known, sure, SVN fell from favour very quickly for good reason. But it had a few years in the sun. Not nearly as long as Git has had at this point.

There were also many holdouts in places that didn't need complex merges.

Having a fixed merge cadence strikes me as both utter madness and totally inflicted nightmare, though. If you're going to merge on a fixed cadence rather than when things are ready, you almost might as well have people push straight to trunk.