According to some reports, teams are not allowed to sell NFTs because the NFL has a strategy in the hot and cold market for sports digital trading cards and art.

The National Football League (NFL) temporarily restricted its teams from selling non-fungible tokens (NFTs) and sponsorships to cryptocurrency trading firms. Based on some reports teams are not permitted to sell NFTs as the NFL has a plan in the hot and cold market for sports digital trading cards and art.
Even though there are different sports leagues like the National Basketball Association (NBA) and major league Basketball (MLB) have started their move towards digital assets, the NFL is taking precautions and are careful before taking those restrictions off. At the present, crypto, NFL will let the teams to connect with companies that are not linked in trading. The NFL is a professional American football league, with 32 teams equally divided between the National Football Conference (NFC) and American Football Conference (AFC).
The clubs are not allowed to sell within the club-controlled media, advertisements for crypto with initial coin offerings (ICOs) other crypto sales and media category can relatable to blockchain, digital asset or as blockchain company expect as presented in this policy. This information was shared by someone anonymous, blockchain is known as a digital ledger whose technology drives and powers cryptocurrency and NFT sales. There are “companies whose primary business is providing investment advisory and or fund management services in connection with cryptocurrency, provided that such advertising sponsorship rights are limited to promoting the company’s corporate brands,” says Thathletic.com
This decision by NFL was made after a specific amount of crypto, blockchain and NFT endorsements already done by a couple of top athletes and teams. Tom Brady, Super Bowl champion initiated his own NFT company, Autograph after signing a long-time partnership along with his and FTX. Other than them there is Trevor Lawrence an American football quarterback got his signing bonus in the form of crypto with Russell Okung an American footballer he gets half of his salary in Bitcoin.