Once someone is here, sending them back is a challenge.
And there aren't a ton of well-established people from western countries clamorimg to come here. There are some, but the majority are less established people--students, etc. It's a higher-risk demographic than you imply. Entrepreneurship is inherently quite risky, and there are plenty of unemployed people in tech.
Unemployment is not pleasant in the US. I'm inclined to believe that most people from a Western nation would up and leave willingly if they weren't having much success, and that people from less developed nations would too if they weren't able to claim benefits. Being an immigrant isn't easy after all - if you're going to be unemployed it's probably easier to be unemployed in your home nation where you have a support network.
And there aren't a ton of well-established people from western countries clamorimg to come here. There are some, but the majority are less established people--students, etc. It's a higher-risk demographic than you imply. Entrepreneurship is inherently quite risky, and there are plenty of unemployed people in tech.