Yeah, sure, let me see what I can do to convey this stuff. So first of all, the system I built was not based on BPMN at all. It was built from scratch and adapted over many years to suit the wide variety of use cases needed. It was still a reasonably generic workflow system, but by being something in house we were able to make it have the actual features that would get the job done, as opposed to grabbing something off the shelf and praying.
My core criticism of BPMN and most workflow systems - like say Camunda - is that they are simply a kind of glorified chart execution system. In general, they are completely disconnected from the actual system they are meant to control. They started from the same kind of modeling background as UML, and have historically had trouble IMO by effectively standardizing first. There was a lot of speculation about the value it could bring. On paper it might seem like the right path: create a visually oriented tool for describing business processes. Focus on the visual language that subject matter experts might be able to understand. Then create a standard for it so that a variety of tools can consume it. One of the problems you see is that the early versions of UML/BPMN were really about a shared visual language for communication purposes. Then as the hope of making it work through automation came into play and a variety of enterprise vendors got involved. Both UML and BPMN went through revisions into order to give them execution semantics to actually run. It was also happening during peak XML/WebServices complexity explosion was happening. This also dramatically increased the complexity, in many ways making a kind of worst of both worlds. Its no surprise to me that the AWS step function system is not based on BPMN, but is quite simple in comparison.
If you want a gruesome inside look of what creating a standard through OMG is like, I find this tale about CORBA to be a good example of the kind of insanity that happens when you make a standard from vendor soup:
https://queue.acm.org/detail.cfm?id=1142044 there's a lot of "castles in the sky" kind of thinking. Here's an account around UML that echoes the similarities
https://tratt.net/laurie/blog/2022/uml_my_part_in_its_downfall.html. A lot of dreaming of how to model the happy path of processes without actually building something and using it and making sure it actually worked. A lot of kitchen sink acceptance of feature requests without a simple coherent vision.
When I built our workflow system, it was a completely different sort of process. We started with the simplest thing we could build - a kind of simple flow chart/state machine that was built as a functional system first. As we built out the larger system (like I said, it was a complete loan automation system), and as we were trying to handle the problems of a real national mortgage lender, the system was built to solve the actual problems in ways that would actually be used/useful. Where it ended up was dramatically different than something like BPMN.