[andriamanitra]

Because the fixed cost of deploying infrastructure (digging the fiber to the house) is extremely expensive compared to the marginal cost (of serving data over an already installed fiber). 20 different companies all digging their own fibers to the same house would be tremendously wasteful.

https://en.wikipedia.org/wiki/Natural_monopoly

[slopinthebag]

But you wouldn’t get 20 different fibres, just one sold to 19 different companies.