In the '60s, AMT was heavily subsidized by the auto companies through the promo business. When that dried up, the flow of new models slowed down. Today, you have to pick a winner.
I wonder if the term "subsidized" isn't a bit of an overused misnomer though? By the 1960's, AMT Corporation's 3in1 Customizing and Trophy Series kit sales FAR surpassed their promotional model business--even when factoring in the sales of what began as promo's as flywheel motor equipped toy cars that were merchandised through hobby shops (alongside their kits), toy stores and variety stores.
Consider also that there were other companies producing 1/25 scale promotional model cars aimed at the auto industry and new car dealerships: Cruver Plastics Company in Chicago, Product Miniatures from Milwaukee, Ideal Models (soon renamed JoHan), SMP in the Detroit area, and the "Johnny come lately" Model Products Corporation. While all of those outfits produced promotional model cars at some point in the 1950's onward, the only promo I can think of that was "subsidized" at the tooling level was SMP 1911 Prototype Chevrolet, which tooling was paid for by Chevrolet, and destroyed by the terms of their contract with SMP once the specified run of assembled promo's along with a supply of kits had been produced.
What did happen though, was a tremendous amount of cooperation between the automakers and the various model companies then engaged in the development, manufacture and sale of promotional model cars for distribution to car dealerships. Consider the advantage of being privvy to what next year's new cars were going to look like, a year or so in advance, not to mention the tremendous trust that had to be established between automaker and plastic model manufacturer, to keep those new styling features confidential until new model introduction time! That cooperation alone had to have meant a great deal in terms of costs not incurred at say, AMT. But in any event, it was the model companies who (with the exception of the above-mentioned '11 Chevy) stood the cost of development of the tooling, against pretty much guarranteed sales numbers.
Another interesting thing is, AMT wasn't in the "driver's" where promotional models were concerned, prior to 1958-59--that position probably had to have been Product Miniatures (PMC), who had a much bigger deal for several years with Ford (producing not only Fairlane Hardtops, but also sedans, station wagons, even the first 1/25 scale Ranchero's), in addition to being pretty much the first (and only -- until 1958) supplier of promotional models to Chevrolet, then firmly ensconced as "USA-1". Again, as with their Ford promotionals, PMC did multiple body styles, and was the first producer of 1/25 scale Corvettes, beginning in 1954-55. Additionally, PMC produced their promo's for Ford and Chevrolet in a wide variety of paint schemes, playing into the need of dealers to be able to show quickly the range of colors and body styles in the days before mega-new car dealerships. In addition to their promotional model car business, PMC had a long-standing relationship with International Harvester, doing promo's of IH pickups and farm equipment in plastic, and a similar gig with Allis-Chalmers, the then prominent Wisconsin farm tractor and implement maker.
JoHan, of course, was the smaller of the three, having to be content with doing promo's for Chrysler, Nash/AMC. Hubley was still even smaller, manufacturing only a handful of subjects.
Of course, the big change came in 1958, when AMT's management bit on the idea of offering their promo models in styrene kits, with the added customizing and racing accessories we young boys went for in a HUGE way when those first 3in1 kits hit store shelves in the late spring. AMT had dabbled with kits before, offering promo's and flywheel toy car spinoffs as knocked down kits, but those had only limited success--they were more "build your own toy car" than anything like a model car kit, and weren't particularly popular.
But, the bottom line is still, from everything I have ever read or heard said to me, that there really wasn't any direct subsidizing of promotional model car tooling--those seem to have been an entrepreneurial game from beginning to end.