Monopolies can have negative effects without trying to extract monopoly rents.
The competition between BT and Sky massively increased the TV rights price for e.g. the premier league, so the clubs got much more money. In theory, they used this to buy better players etc and increase the quality of the league.
Although you now have to pay twice, the quality of the product has gone up. So it's not a zero-sum game. You can argue that you don't think it's worth it, but that's an opinion, it's not true that it's an inherently worse situation.
Until they entered into a rights sharing agreement.
Also worth noting that the rights sharing arrangement on Sky's end is... <drumroll> ...mandated by a settlement from a previous anti-trust case!