Erm, I don't believe it has much to do with performance.

Less people use it due to readability and maintenance issues. The tertiary operator is generally seen as a bit more obtuse than the simple if statement. Your own if statement wouldn't be quite as bad if there was better formatting of the code.

In the end the compiler will generate the same code either way, optimized as far as you tell it to.

Also, this doesn't really belong in code review. This would fit far better in the noob programming forum.