The carbine is a bit of a wonder with a wild history. The reason that every part is marked is because the carbine was one of the very first almost totally sub-contracted procurement in military history.
Many many many machine shops, small and large, were tasked with producing one of the 45-ish parts of the carbine and the government wanted each part stamped with the origin and destination so that any sub-standard part makers could be quickly identified and removed from the procurement stream.
I used to purchase carbines by the armload from surplus arms sellers in the late 80's. Each one was like cracking open a pack of baseball cards from the 40's. A rare Rock-Ola trigger here, or an IBM made stock there, I would cherry pick the best bits and either restore the gun to "factory correct" or build it back up and sell it as a "shooter".
Those were the days... would buy them for anywhere from $175-$250 and then often flip them for $300 or so, after removing all of the high dollar "rare" parts and replacing them with unmarked parts. The so-called factory restored guns would often fetch closer to a grand, depending upon the rarity.
At the height of my insanity, I had one from each of the ten manufacturers in my private collection and was buying/selling 5-6 of them a month, phone combing all the "local" gun shops and trolling every gun show. Half the stores had me on speed dial to call whenever they got any in.
Alas, the AR excitement of the pre-Y2k years saw me parlaying a lot of my carbine "wealth" into cheap AR's that I was then flipping to my accountant/lawyer buddies for top dollar in the run up to the "chaos" of the new millenium.
Still have a couple of carbines though. A really clean Inland that I shoot and my favorite... a completely original IBM/AO that was given the German Rural Police at the end of WW2. I love that that one can be placed to a time and a place in a way none of the others could be. Probably sitting on about 10k .30 cal carbine rounds too.
Fun fact: The only piece of durable military equipment made in greater numbers during WW2 than the m1 carbine was the ubiquitous M1 steel helmet. Over 6 million carbines were made between 1943-45