Engines - The "weight to burn" thing was what I was told at the time, by someone who was probably unaware that the program had lost the plot.
Industrially, the Mauser was a bit of an orphan - the company that was supposed to build it for JSF had started as part of Hughes, then was Macs, then was Boeing, who finally sold their gun line to ATK. I suspect they made a lot more money from the Army than the AF and doubt that they put up much of a fight when GD (I think it was GD by then, having previously been GE) launched the offensive to throw them off JSF. For GD in Burlington it was pretty existential.
Gatlings were more competitive with multiple guns (the typical pre-missile setup) than with a single heavy cannon. As noted, only the US went all the way with the Gatling, but the time-to-rate issue mandates a lot of ammo in a heavy feed system.