Spammers are better at SPF, DKIM, and DMARC than everyone else

You may be surprised to learn that spammers, being criminals, have no issue with stealing money from others to spend on email delivery fees.

Edit: Proof-of-work "email postage" schemes are similarly doomed - The botnet that zero-day'd your mail servers does not care how much electricity they use.

Criminals yes, criminal spammers no. If they could make money with other crime there would be no point in wasting their time with sending spam.

The point to sending the spam is to enable further crime. Do you really think they don't stand to profit from what they promote? Spam is a business like any other, they aren't going to magically disappear just because their advertising costs suddenly become non-zero. Just like how they found ways of shifting the costs of hosting mail servers onto others, they will find ways of shifting the costs of any "email postage" scheme onto others.

This is very basic mathematics. If they have to do other crime to get their hands on the cash it would cost for them to spam, then why spam at all instead of only focusing on the other, more profitable crime?

Spam by definition is mass messaging. If the price per message is higher than the expected return per message, it becomes pointless.

Spam is advertising for their other more profitable criminal enterprises. It's a means to an end, not an end itself. If the goal were simply to send messages, there would be no content.

And the efficiency of spam is so low, that with a high enough cost per message, it would not be a net gain for the spammers. If you pay a million dollars to send a million messages, but only gain $100 000 from the subsequent scams, then it's a bad venture.