It's been decades...but if I remember correctly, NHRA, AHRA and IHRA all used to have slightly different contracts for their various "National Event" tracks. For some track owners, adding more advertising was a smart thing even if the gate was split 50-50. That track's contract with NHRA might give it all the additional concession sales from a larger crowd. That alone could be very profitable return on the investment in more local advertising.
In this case Billy Meyer is most likely adding to the purse and qualifying $$ to improve his chances of giving his fans a full show. I did it with the AHRA Gateway Nationals in St. Louis. Jerry Haas once told me (a long, long, long time ago.) that I was the first person to ever pay him appearance money. I didn't want another year of only 7 or 8 cars showing up for the 8 car field Pro Stock Class as I had enough fans complain about it the previous year. (and it was probably $100. Jerry lived in the St. Louis area.)
It has to hurt a track owner's future in his marketing area to advertise an NHRA National Event and only have 13 T/F and maybe 14 F/C's show up. The paying crowd remembers. I would be curious to know if BIlly Meyer receives any compensation for the TV viewing audience or if he possibly gets a bigger cut of ticket sales and NHRA keeps all TV revenue. That's the sort of thing that might make him want to increase or improve the show.