Any "in-depth" Insight Into Malware Authors' Motives?

TBH the motives are money plain and simple, end goal is data mining as to personal ID as thats worth money and banking details as with that they can fleece your account in seconds. Some of the ransomware has hit the vulnerable and less PC savvy in "This is Microsoft and we have seen a virus or issue on your PC, give us your Credit Card details and we can fix" sadly Microsoft will never phone or email you to say you have an issue, you would need to raise an issue with them first, they have neither the time or man power to know what your PC is doing.

A really good abstract on malware is HERE its old as in 2007 but the debate and argument is sound, you can read many technical papers HERE

Malware is a moving target all the time and no one direction is locked down to a cause apart from MONEY!