Because forcing exclusivity is anti-competition. If you want a competitive ecosystem, you create laws that do not allow the largest player in a market to force customers to exclude their competitors in another market in order to use their primary product.

If you're a libertarian, you would think that's fine, but in a libertarian world one company would have 97% of the market, and if you wanted to use their electricity, you would be forced to buy your food from them.