You don't think the proliferation of inexpensive dogshit IoT products from the Far East, running already-10-years-out-of-date versions of Linux (bonus if it has a hidden Telnet daemon with hardcoded root password!), hooked to ever-expanding 1Gbps residential fibre lines, has anything to do with it?
This represents like 75% of surveillance camera systems out there btw.
I think the increase in 1G residential connections is a bigger factor than the IoShit products. I don't think botnet node counts are getting that much bigger, but the amount of garbage each one can push certainly is.