It is hard to fathom nowadays with decades-long "jobs for the boys" projects like the F35, but weapon making, especially in wartime, can be greatly accelerated and benefit from skunk projects carried out by small teams. (note however that the inherent difference in complexity between a major weapon system - a fighter or tank - circa 1940 and 2020 is massive).
First, look at the genesis of the AK47, basically a "tank dude's hobby project".
Second, as per wiki, there was a competition for the MG42's design and the winner got awarded the order. It wasn't just a case of awarding the whole process to one company.
The chief engineer took non-arms metal working experience and applied it to make a better design. Between better, cheaper and less time and raw material to make it, why not pick the best entry?:
Dr.-Ing. Werner Gruner, one of the leading design engineers with Großfuß, knew nothing about machine guns when he was given the task of being involved with the project, although he specialized in the technology of mass production. Gruner would attend an army machine gunner's course to familiarize himself with the utility and characteristics of such a weapon, also seeking input from soldiers. He then recycled an existing Mauser-developed operating system and incorporated features from his experiences with army machine gunners and lessons learned during the early stages of the war. Being made largely out of stamped appropriately hardened carbon steel metal, the new design required considerably less machining and fewer high grade steel alloys containing metals that became scarce in Germany during World War II. It was much simpler to build than other machine guns — it took 75 man hours to complete the new gun as opposed to 150 man hours for the MG 34 (a 50% reduction), 27.5 kg (61 lb) of raw materials as opposed to 49 kg (108 lb) for the MG 34 (a 44% reduction) — and cost 250 RM as opposed to 327 RM (a 24% reduction).
Note that the entry of highly-skilled manufacturing firms into a domain which they do not have prior experience in can be highly disruptive to that domain, c.f. the Apple iPhone, Tesla or SpaceX.
This seems to have been what happened with the MG42 and there was certainly a lot of German "pull" demand requesting new weapons from all over the German industrial spectrum. And the opportunity cost of asking a non-arms metalworking firm to bid in a design competition would have been low.
See also also Porsche, which got pulled into the tank-design business.
Finally one can't mention the MG42 without mentioning that its descendent is still getting built today.