IndyCar probably doesn't have any say in it. NBC usually carries golf (PGA) on Sundays. (Never mind, CBS carries golf usually, not NBC, so I'm confused.)
ABC doesn't want to broadcast all the races obviously for some reason. Even though their coverage isn't the greatest.
Looking at TV guide NBC has local programming on Sunday through 2:30 in competition with the Sprint Cup race, and then at 3 or so NHL (hockey) comes on. This is usual for them. They have F1 as well and it's trapped on NBC sports network..
That was done after ABC was reluctant to cover the whole season, but TG made sure to sign with the lowest rated channel Possible to ensure indy will struggle to survive for the years after he gets invitably sacked.
Leigh Diffey is a good commentator, but better suited to sports cars, Brian Till is awful, Townsend is okay.
Problem is rather than go for somebody that actually knows Indy, NBC wanted a foreign voice. They ought to move Leigh down from lead spot to analysis, and put somebody in the lead spot who actually knows what they are on about, Just for the love of God, NO NEIL CROMPTON!
The situation back then was very problematic. Neither Disney nor the News Corp. had intentions to cover the season on any of their channels. Even if both covered parts of the season there would have been races without any coverage.
This 10 year deal with Versus and ABC at least guerantees that every race is covered, rather then having to negotiate every coverage over any race and potentially having races not covered at all. It would have become the Indy500 and some random races using the Indy500 cars then.
Versus became NBC Sports Network. Now I wonder if such a situation was covered by the contract. I bet there is with something like "if one of the contracted channels gets bought by a different network, the other channel has to agree on putting the races on a different channel of the network" Pure speculation of course, but that would explain why NBC didn't schedule one or two races on the main NBC one. Especially when thinking of the rumours that NBC is interested in covering the Indy500 from 2019 on and ABC wants to continue its contract. A bit of muscle playing.