The point is that AWS removes friction and Elastic chose to add friction. They're chasing big Enterprise hard and it doesn't seem to be working out.
Big Enterprise will not require billing through AWS (disclaimer: employed at a large enterprise, buying ~$900k software license currently). They’ll have an accounts payable department, a procurement process, and someone to cut a check or ACH to Elastic monthly/annually.
Would you want to be beholden to AWS' whims? You might as well be a Walmart supplier at that point, constantly dragged out to Bentonville having to make your case for every penny of your costs. Amazon has proven its model (all about scale), how it operates (your margin = our opportunity), and you partner with them at your own peril.
I'm suggesting the thought process to shift from, "Ahhh, those Elastic guys and their bad decisions!" to "Hmm, well, tough decision to make [forgoing revenue through AWS] but I understand why they made it".
It's a big deal for a lot of companies to be able to pay the cloud bill in one place. Elastic used to provide the availability to pay for the Elastic cloud subscription through AWS' Marketplace. Elastic stopped this when they changed their pricing at the beginning of 2017 and we (my last employer) were negotiating a contract with them at the time. AWS billing was a hard requirement for us because it made it a lot easier on us from the finance side. We walked and I know a lot of others who did too.