The customer doesn't want this. It's a full sized car with only two doors and two seats. If a vehicle doesn't have four doors it doesn't sell.
There is nothing stopping Cadillac from making the same Fleetwood they made in 1994 except the customer. The market for that car does not exist. You blame government regulation, but what you should really blame is consumer preferences.
in the US, besides trucks (#1 seller) a big seller is the mini SUV/CROSS OVER type vehicle. the market doesnt demand big 4 door sedans. the only ones out there are for the well to super rich that are worth a damn...
from the cheapest decent 4 door sedans
maxima/honda accord
CTS cadi 5 series/e class
A8, 7 series, s class etc etc
porsche, Aston martin, maserati
then the peak for high end large sedans that do ok...
bentley, rolls etc maybach
average person really doesnt even want a 4 door large car anymore. i love em cuz i am old school, id love to a big ole jaguar boat