There are lots of people applying for a job right now and employers cannot review every single resume and try and contact everyone. That said your Cover letter

There are lots of people applying for a job right now and employers cannot review every single resume and try and contact everyone. That said your Cover letter and Resume should be tailored for every contact (obviously, you likely do this already). If you are being Interviewed the interview is pretty much over; you have to Interviewer now. As you said you are bad at interviews this is likely the your problem. Apply for other positions that are not in the Fortune 500 list. Keep trying and change the companies you apply for and try and have fun. Hardest part.