vvw I feel your pain :(
What's with your passwords? and then with your hosting? and with your computer & software?
I understand some hackers choose sites for their content to deliver specific messages to specific targets. That's all I can say related to your content being like bait, I can only think about other factors. DMCA complains work, you just have to follow the guidelines and wait, no clue on why you never got a response from G.
[1.] Having used diff systems and technology (CMS, DB and even plain HTML) there must be something wrong with your passwords and usernames, are you using the same pass every year since you began working with this? if not change it every now and then!.
[2.] The other possible vulnerability would be your hosting. Are you on the same company while all the problems ocurred? I've seen cases where the server is compromised and the best solution is to change hosting. If all those problems happened while on the same company, change now, what kind of response did you get from them? I'll say find another one.
[3.] Are you using the same computer? Perhaps the problem lies on your computer, be it spyware or whatever catching your passwords as you type or compromising your FTP sessions. Are you using SAFE INTERNET? or WIFI on non secure networks? avoid it!. Are you alone on this? any "partner" perhaps trying to ruin your thing?
As for technology, every CMS has a vulnerability from time to time. Make sure you have the latest stable version or try another CMS solution. You mentioned having problems even with plain HTML, that's where my other questions come to mind. You also mentioned that html being produced by WP, if everything is on the same server then if WP gets compromised your HTML will also be compromised.
As for starting over again, it happened to me in several projects. I lost a finished book I was editing for print, also lost 4 months of hard work of programming and had to start from scratch both times. Pretty shocking to me, felt bad and kinda sick for days.
There are diff opinions but: diversify, make backups, review your sites every week and don't put all your sites on the same server.