Tbf ROS is a pretty old project. ROS1 dates back to 2009 iirc. A lot of technologies didnt exist back then. Even ROS 2 is now relatively old. The way I see it is that we have since learned a lot about software engineering. I dont think using cmake with catkin and relying on debian packages makes much sense now a days. But back in 2009 I can see why we would have to do it. Heck using catkin to share c++ code by copying the code into a local workspace was so much easier than having to figure out which set of systemwide packages and which cmake incantations would work correctly. Today, however we know how to do packagemanagement much better via tools like cargo. However some core ideas like pub/sub,micro services, message definitions, message recording and playback will be part of your stack.

With regards to startups in general though. Having worked at a few Ive noticed that at the earliest stages the goal is for a few individuals to build quickly. Often this means certain framework choices that may not be suitable to scaling. As one scales one has to then evolve the architecture to ensure developer velocoty. This may mean rewriting everything. Im not surprised that people are rewriting ROS internally. At the end of the day there are a few good ideas in there, but at some point one has to acknowledge that implementations were lacking.

Personally if one were to write a middleware framework in 2024 Id go with rust, mcap, zenoh, rerun and possibly use ecs instead of topics.