From Jack on Patreon:
"Why did the US go on to develop the M1 Garand instead of continuing development of the BAR? With the BAR you already have a self-loading rifle with as much firepower as later battle rifles of the Cold War (such as the M-14), including detachable 20 round magazines. Why not just try to make a lighter weight, possibly semi-auto only BAR instead of starting over from scratch?"

There was one proposal to do something pretty much like that in 1919, but it was rejected by the Infantry-Cavalry Board for a couple reasons:
- The BAR was not really capable of manual operation in case of malfunction
- The BAR was too heavy
- The BAR was not clip-fed

We can see more by looking at the 1921 RFP for a new US Army semiautomatic rifle. Among the requirements were a strict weight limit of 9.5 pounds and a requirement for a clip feed holding between 5 and 10 rounds. The US military saw box magazines as undesirable for a service rifle, as they held the rifle too high up off the ground, among other reasons. In addition, they rightly saw that it would not be practically possible to reduce the weight of the BAR by 40% and retain the proven, reliable characteristics of the design. While it's not explicitly stated anywhere, it seems like the idea was that if Browning thought he could produce a shoulder rifle version of the BAR, it should be proposed as a new design alongside the Garand and Hatcher/Bang systems then in development.