They never enforced the rules, so guys started going bigger and bigger. Now they have about 8 cars or so that they are trying not to completely alienate and tell them they can't race with something they've had for a few years, so they are trying to level it out to keep more guys from buying them. The motors that guys like Brian and Guidace are running are nearly as expensive as a good big block and need rebuilt in half the laps. With the enforcement of the proper rules, there should be some growth in the division because guys won't be able to price themselves out as much. The next thing that needs to go is the 18 degree heads, as the price tag on those is completely outrageous.
DIRT made moves to get rid of the big small blocks back in the mid 90's when 410-430s became the hot ticket. They were really fast, but they were also insanely expensive and pretty unreliable. And some of the better financed teams were doing some kooky shit to them.
The RoC tour allows you to run basically any steel block motor, though.
The DIRT 500 motor that they keep pushing might get some people into the class, too. I don't know how competitive they will be, but in the dead of summer when the tracks are slicker than whale snot I don't think it'll matter much.