Not a ransomware creator but I understand the economics at play. Ransomware is more profitable than sending spam, unless you're spamming to spread malware.
The value of individual installs has historically averaged at significantly less than a dollar each, ransomware is bringing that way up.
You aren't going to stop ransomware unless you figure out a solution to all other malware, or invent a more profitable scheme. People need to do something with their bots and ransomware is always going to make more money than spamming from bots that haven't been able to inbox anything for 5 years.
There's simply no way you'll stop enough people from paying to make viagra spam beat ransomware.