There is a theory that aliens are also fallen angels. Although they lost their angel status and powers, such as traversing through the universe in a flash, they still retained their immense knowledge, and in turn, built such machines to aid them in their travels.
Think about it. During the past 70 years or so, mankind has made more technological advances than in the entire history of the human race.
As for why they're here. The fallen angel aliens are unable to reproduce, so the human reproductive system is fascinating to them. Thats why so many stories of alien abductions involve probes and examinations of the reproductive system.
In exchange for power and technology, aliens may abduct humans and use them for non-lethal research experiments.
Anyway, on topic, I need to see some evidence of them making their presence know. Verifiable evidence.
Also, I'm not giving too much credit to Mr. Schnoebelen, as his primary publisher is/was a hate group and he's made a ton of claims I find kind of ridiculous, but I'll read up on him more tomorrow.
As for technological advancement, I'd attribute that to each discovery enabling more discoveries, speeding up technology in a ~Quadratic manner. On the angels bit. I'm not really religious and don't want to start a war with my second post, so I'll stay away from that. My guess is the alien abduction stories are more because of a Freudian subconscious or something.
Also, could you try to get in touch with these aliens and get them to hook me up with some tech? My computer's getting a bit slow.