Please answer a question about the following article about Premier League:

The TV rights agreement between the Premier League and Sky has faced accusations of being a cartel, and a number of court cases have arisen as a result. An investigation by the Office of Fair Trading in 2002 found BSkyB to be dominant within the pay TV sports market, but concluded that there were insufficient grounds for the claim that BSkyB had abused its dominant position. In July 1999 the Premier League's method of selling rights collectively for all member clubs was investigated by the UK Restrictive Practices Court, who concluded that the agreement was not contrary to the public interest.

Why has there been a several court cases against Sky and Premier League?
The TV rights agreement between the Premier League and Sky has faced accusations of being a cartel