For $15/hr, you do not get top quality C++ developers from any corner of the world. I know - I've worked for companies that have tried. You tend to end up with a spaghetti code base utilizing crappy open source or shareware libraries that a cousin produced. Then, you try and scale, and need to bring people that actually know what they're doing.

2 years in at current job, where most of the work was done by offshore devs, company now has a team of onshore developers to fix all of the performance and stability problems.