Toyota and Subaru have massively cut their motorsport budgets over the past 10-15 years.
toyotaracing.com
NASCAR, NHRA, USAC, and Off-Road
Toyota wants to sell Trucks and Camry's against other Trucks and Fusions/Impalas, that's the money maker. US road racing is slim pickings as it is, why blow millions of dollars on a campaign that only a few hundred thousand people will ever pay attention to? (Off-Road falls into this category but I assume it's a cheap sport to run based on what I've seen, relatively speaking of course)
NASCAR even with flagging numbers in recent years still pulls >5million viewers per race and over 70 million unique viewers through the season. Indycar struggles to pull 500,000.
In a more perfect world NASCAR would be a little more stock and there would be a handful more road courses...
In any case it's no wonder why we're not seeing the FRS take checkered flags imo. There's a diminishing benefit for automakers to participate as information wins buyers dollars today (reviews, tests, forum posts, etc.) not racewinners.
As said above, the Miata didn't roll into a Spec race the first year it was produced. Toyota is pushing them over in massive numbers, there will be more total Toyobaru's on US soil in the next few months than S2000's. As the guys who know how to make racecars out of regular cars figure out what's really necessary to make these things reliable on track and competitive organizations figure out how to class the cars competitively the scene will grow regardless of Toyota/Subaru's level of support.