The problem is that the jobs lost to imports are more visible and more easily associated with imports than the jobs created by more exports and larger capital inflows.
The problem is one of perception: jobs lost to imports or outsourcing are more visible to the lay public than the jobs created by exports and insourcing, even though they do tend to balance out.
This conclusion is not obvious to most people because jobs lost because of imports (or outsourcing, or factories relocating abroad) are more visible and more easily associated with trade than the jobs created by exports.