I guess if they're big enough they should be working on moving off of amazon SES for emails and warming up ip addresses? Otherwise they need to keep a markup on top of amazon.
Edit: didn't realize people were paying resend $20. AWS already exists at a low price and people pick them anyway, i'm sure they're fine.
It's very easy to get started with Resend, and they have a free tier that basically works for any bootstrapped project, and by the time you have to upgrade, you can pay $20/m.
And if you want a SaaS like experience for your own AWS, there is wraps.dev ;d
I'm betting a non-small chunk of these are users AWS wouldn't let out of sandbox mode.