EU also has a lot of immigrants as well, and also an even bigger culture of education and intellectualism. Why then don't they have more successful tech companies?

I think you're omitting the giant impact of the FED, wall street, power of the USD world reserve currency and the VC investor incentives of risking billions on ideas that may or may not be profitable, with the low risk for investors if their investments don't pan out.

All stuff that doesn't exist outside the US.