Sending money overseas only benefits the single buyer in the short term. Keeping it within the country increases the wealth of that society leading to better services for all citizens.

Here's a counter example:

A island nation with highly accessible fisheries populated by 100 people in the middle of the ocean could spend their labor on building a CDN or fishing.

If they use other's CDNs, the money they sent would be used by foreigners to buy their fish, which could be produced very cheaply. Building their CDN means forgoing their fishing opportunity. Building a CDN means they can now sell their CDN services cheaper than it would have cost them to run a website to sell their fish, but the benefit is marginal compared to the income they would have received by focusing their labor in an industry where they have comparative advantage.

They must choose only one because they have limited labor.

...Land, labor, capital and technology is wealth, and money only represent a claim on that wealth.

The comment being replied to specifies that blocking and building would be a beneficial activity for all countries to participate in.

Taking your argument to its extreme, entity should trade with any other entity.

Trade walls hurt everyone in the long term.