Because PF3 does NOT do anything with AI that could make them go through your aircraft but there is a setting in FS that turns off crash detection, have you changed that perhaps?
Also, did you try the PF3 demo before making your purchase? There is a HUGE prompt advising you to do so on the OnCourse Website Store page.
Rather than giving up so quickly why not let us try and help you through the issues... I'm sure it can be easily rectified if you give us a chance. There are plenty of happy users right here on the forum who have been using it for many months now.