I charge $1/month to send email on my email service. There’s a reason for that. It’s because it’s the smallest amount I can charge, and spammers are unlikely to pay anything, no matter how small, to send email. If they do, and I catch them, I’d probably be able to get their payment account suspended. So, I understand why this could be a good approach to combatting spam. Here’s the problem with Twitter doing it:

• Elon has full control over the platform. It’s not like there are other providers that will block him if his users send a bunch of spam. He also has the ability to revoke all the messages that users have sent once they are discovered as spammers, whereas with email, once spam is sent, there’s nothing I can do about it.
• Email is actually useful. Tweeting is just self promotion. No one coordinates their doctor appointment with Twitter.
• Spam is basically the only thing keeping Twitter looking viable right now. Their users are leaving. Their advertisers are leaving. It’s maybe not the best time to be pushing the spammers away.
• Elon’s whole mission or whatever is supposed to be “freeze peach”, but this goes against that. The “digital town square” where “everyone has a voice” can’t have a price tag.