I don't think the league blocked him, I thought he was just flirting with the idea the whole time and would never actually commit?
Yeah the NFL didn't block him, he was outbid. He later claimed that he was grateful he didn't win the bid, because after the failure he decided to run for president.
https://www.si.com/vault/2016/02/11/general-trump
Trump's football interest outlived the league. In 2014 he even bid on the Buffalo Bills. He says he offered $1 billion, all cash. Fracking magnate Terry Pegula landed the team instead for a reported $1.4 billion. "I'm glad, because if I bought the Buffalo Bills, I probably would not be doing what I'm doing now, which is much more important," says Trump. "I would have done a good job with the team, but I wouldn't be doing what I'm doing now. So you understand. Now, that's today. I'm No. 1 in the polls. Ask me that question in two months; who knows, right?"