Target is out after this year in IndyCar, and 2017 will be their last in NASCAR. They are "streamlining" their marketing practices, which usually means slashing the budget, which usually means the most expensive things go first, like racecar sponsorships. I doubt they are going to bail on one series just to jump on board with another, particularly when their goal is to reduce capital expenditures.
Half the Target stores in Vegas have closed in the last couple of years, so they aren't only dying north of the border.