Except for literally causing financial harm to the elderly that they prey on. With email there has always been extra scrutiny, after all it is the tech literate who were and are most likely to use email. And by literate, I mean can turn on their computer and visit Gmail. I doubt we will see the similar scenario with email due to spam being commonplace since the beginning.
Not to mention every other person is actively bothered in the real world by a real alarm instead of just scrolling past while checking their email. Email spam vs robocalling is not even comparable in terms of the effects. I miss real phone calls from people, such as job offers, due to spammers forcing me to send everything to voicemail. I'm not a hateful person by any means, but I honestly wish the absolute worst on anyone who is behind scamming robocalls purely due to the amount of minor annoyance built over time.