There are plenty of homebrew Flipper apps out there. In fact, I'd argue a majority are homebrew at this point.

What's more unknown is how many haven't been published because they're running on Flippers used in a traditional business or manufacturing environment rather than for hacking - profesionally or recreationally.

Me, I looked at the cost of those devices, how established and stable the hardware is (i.e. is it likely to change unexpectedly or disappear tomorrow), how quality it is (i.e. whether it come from some nondescript company in Shenzhen), how stable the API is, how well documented the SDK is, how well supported it is, how vibrant the community is and how much we have to invest on top of the cost of the devices to turn them into the production tools we need, and I made a business case for a fleet of Flippers rather than laptops on the production lines at my company. And it was approved.

Surely other companies have decided to go with Flippers as a rational business decision, but you'll almost certainly never hear about those Flippers or the custom software they run.

If I get permission from the higher-ups, I might rip out the company-internal code from my app and release it under some open source license for our customers, or anybody who wants to use our products on the go. It's 95% there and it is useful if you have a need for what we make, even without the advanced functionalities. But at the moment, it makes calls to undocumented features and has a hard-coded extended API unlocking code that makes it impossible to release.