It didn't get another ad until it was a proven success, and at that point there weren't as many episodes left to run. There would not be another one until the fall.
Much of the early merchandise was based on the mannerisms of the first season. Throughout the entire series, Bart has only said "Eat my shorts" twice as an actual comment and not a joke about how he's "famous for saying it." There was barely anything to base entire video games like "Bart Simpson vs. the Space Mutants" on, making them awkward and barely connecting to the show's feel at all. Ditto for the Simpsons arcade game, which still turned out great, yet had bizarre easter eggs like Marge's hair falling off to reveal bunny ears. Odd as it may sound, that was a real idea the writers had discussed, but never committed to.