Why do SaaS companies not put up screenshots?

This is a new trend. Notion, figma, airtable do this. These are all modern day SaaS winners with great design teams. Most SaaS companies don't take design seriously. Cause they don't need to have great design to get customers.

Maybe it's a concern about screenshots not matching current versions of the product, but that shouldn't be a concern on the main product page or home page.

Are screenshots required for good marketing? Are you the market they are selling to?

Some do, some don't. It really depends. I'd suggest it isn't bad marketing, but it can often be difficult to make a screenshot look appealing to the buyer. It might look appealing to the user, but that is often a different person.

If it is so consistent in the industry, I doubt it's by accident.

Sometimes the SaaS is so old that a screenshot would stop users signing up.

Doesn't mean they're not the best at solving the problem though.

Even AWS almost never has a screenshot of a particular product in use, even on its main product page.

They want you to sign-up.