I'm hoping somebody who is more technically knowledgeable than me can figure out who was/is spamming. I know it's not that easy to attribute the transactions. Chances are we could at least get a source IP address, and then work from there...
Pretty much this. A lot of the wallets, both online and standalone are not that smart with respect to fees and have been manually adjusted to higher levels and haven't been adjusted back down. Anyone running bitcoin core/qt which has a dynamic fee estimator would have noticed the drop in recommended minimum fees to just over 100 satoshi per byte over a week ago.
This site has been showing it for a while too if people have been paying attention instead of using some braindead default:
https://bitcoinfees.21.co/