AGPL don't stop nobody from monetizing anything, they just gotta make their modifications public.

If you're anywhere close to a technical or developer space it's pretty clear how making your entire codebase public could negatively impact a monetization strategy. So yeah you're right that AGPL doesn't explicitly prevent monetization (other than "pay us for the source code" stuff of course) but in practice nobody with a serious monetization strategy is going to be releasing all their code AGPL either.

> but in practice nobody with a serious monetization strategy is going to be releasing all their code AGPL

Which fulfills the developer will of attracting higher quality users that plan to collaborate with him. You got it right :)

You got something wrong tho, If you're anywhere close to a free software/open source space, you should know that using his AGPL SQS replacement, the only thing that would need to be public is whatever you change in it, not the things you use it.

Also, is there really any money left in message queues?

Every man and his dog has made a message queue with Postgres. Message queues are everywhere on github and often posted on HN.