It's probably the fact you still haven't finished the degree. Requisitions tied to Univ level requirements etc. Even if they don't say anything, hr at companies of Amazon caliber will most likely discriminate you on that.
Why not. It's not like HR/given department pays for your trips out of their salaries. They just want to have the headcount for an interview.
Edit: From the people around me, and the companies I've been, big companies like that will discriminate you on age far less than not having a university diploma / other academic accomplishment. Finish that degree as fast as you can.