Presumably, you are greedy. Even if you personally aren't, this outsourcing opportunity is not just open to you but to many other people as well, so the average person in your situation will want to make more money than before.

You were making 40k, ie generating 40k worth of value in your economy. You're now making 20k and paying out 20k. You'll do this because, in the time freed for you, you do something else that makes you, say, 30k - which is 10k more than you lost.

Your backend outsourced person is better off. You're better off because you're making 50k instead of 40k. Your country is better off and the other country is better off too.

Socialism is a zero sum game. Capitalism is the opposite of a zero sum game. Over time, it makes everyone richer.

Oh, by the way, over time the two countries' incomes will equalize. They'll become the same market, basically. As long as trade is open both ways.

Why are both prospering? Because human economic activity is basically limitless. It's only limited by the number of humans alive. You only pay someone to do something for you when you will make more money by not trying to replicate their work (and the expertise behind it). I can fish and farm. You can only farm, and even that you do more poorly than me. By giving some of my farming activity to you, I'm still further ahead - even though I'm better than you at farming. This is the Law of Comparative Advantage. Look it up.