> Why should the presence of US tech companies mean local tech companies can't compete?

That's not the right question. The correct question is:

Why DOES the presence of US tech companies mean local tech companies can't compete?

And that's the beginning of the discussion. If there is no money to be made, no market will be developed. Block US companies and in a few years you have a booming ecosystem.

Can you answer why US companies are so good at providing value that customers choose them? Obviously things can survive if there's no competition, but why is that better for the consumer?

> Can you answer why US companies are so good at providing value that customers choose them?

Some greasy words. Using VC money to offer subsidized services while capturing the market and killing competition has no relation with being "so good" at providing value, much the opposite.