> Can you give some examples of this happening in real life?

Uber is the canonical example of this, I guess.

> None of the examples I can think of where people criticised the companies for operating unprofitably, such as Amazon retail or Uber, were able to corner their markets.

It's not about people criticising this behavior or not. It's about being factored in the model. The free market model assumes that every participant in the market has the same access to capital, ensuring that every market participant can equally undercut everyone, making this particular strategy irrational, therefore not part of the model.