Casting got a bad name years ago when cheap Spanish handguns, made of "pot metal" were imported by the ton and blew up almost as fast as they came off the ships. The problem was not casting itself, but the material from which they were cast.
There is some notion that the term "pot metal" refers to some kind of alloy melted in a pot. It doesn't. It refers to the material cooking pots were made from, cheap cast iron that was flawed and brittle, and very prone to break under pressure.
But those guns put the kibosh on the use of casting for guns for many years, until Ruger, using good material, and good production techniques, showed that cast guns could be strong and serviceable. (Though many cast Ruger parts are thicker than forged parts used by other makers, in order to have the same strength. This leads to such siliiness as "no one can blow up a Ruger", when quite a few people have, often because they believed nonsense.)
Casting is not always cheaper than forging, but it has the advantage of requiring less capital investment and less of a factory environment. Forging requires large presses that have to be quite literally sunk into the ground, and which shake the building when operated. Casting can be done in a shopping center. Also, investment casting, unlike MIM, still requires machining to final dimensions, almost as much as forging. But MIM, while fine for small parts, is not (yet) feasible for larger units.
A note on the Winchester Model 70; the modern Model 70 receiver, AFAIK, is made from a forging. Pre-64 Model 70's, were machined from bar stock.
Jim