I agree this is a head-scratcher. Just to come at it from a slightly different perspective, SME has always been known for it's engineering ability. The 301 was originally designed and conceived as a motor unit. Why did SME decide to go full retro with a 3012 arm? The 301 withstands the test of time but the arm does not. Mating today's best MC cartridges with the low mass arm is dicey to say the least. Does SME envision that customers shelling out $16,000 are going to install vintage Shure cartridges with JICO styli or today's MM and SPU cartridges? One thing remains consistent; the SME turntables with their conical shaped suspension towers were always ugly (at least to my eye) and as others have noted, the plinth borrowed from Loricraft is likewise ugly. In conclusion, SME should have come to market with a 301 motor unit-only sold in a box just like the original for the end-user to select the arm and plinth of choice. Perhaps they are. Things are murky at best.
You've obviously not been following some of the best systems on this forum. While the arm on the new 301 is not a 3012 (it's a M2-12R), the 3012R has proved it can hold its own with many modern arms including the SAT.