If you give people free web services they're going to use it for spam, porn, file sharing or crypto mining. If even their most basic tier only cost a few quid a year, it would probably stop spam usage by 99%
Not really; they will just sign up. Probably using a stolen card (I assume? I have no way to check.)
Source: have worked for email provider. Have you seen one of those films where one guy fends off hordes of zombies or other "bad guys"? It's like that. Anything that can send email will attract hordes of twats trying to spam the shit out of it. The main difference is that the spammers are more despicable subhuman twats.