they make a lot of money by having big meets. big meets = lots of competition which then starts to attract more and more top athletes. Then they've added their early December meet and last chance meet in the last few years and specifically marketed them as meets to chase fast times.
and what the other poster said about them always having rabbits for the fast heats and being very accommodating to the pros.
There's other fast tracks but for example the Armory is mostly used for youth and high school meets and a lot of the other fast ones are oversize.
If the Armory or Arkansas or Texas A&M wanted to host meets with 50 sections of time trial style racing of every event people would come.
Also you can't forget that indoor is a much bigger deal in the Northeast. So people care and take it just as seriously as outdoor, especially the athletes that aren't gonna make outdoor regionals/nationals, as their outdoor season will end by the time the weather is decent in the Northeast and a lot of teams there don't do the whole "travel to 3 west coast meets every weekend" deal.