I'm almost certain it's because of SLRs and through the lens viewing. Leaf-shutter SLRs were more expensive to make and were more complicated. To get an idea

I'm almost certain it's because of SLRs and through the lens viewing. Leaf-shutter SLRs were more expensive to make and were more complicated. To get an idea how, read about halfway down the page here: https://simonhawketts.co.uk/2016/11/05/kodak-retina-reflex-iii-35mm-slr-camera/ https://simonhawketts.co.uk/2016/11/05/kodak-retina-reflex-i... Basically, focal plane shutter didn't get in the way of the viewer's light path since they were behind the mirror. They were cheaper to make, more reliable, and operated more consistently at the rated speeds. They were almost certainly more durable. Tungsten focal plane shutters can be rated for a 100,000 activations.