I didn’t say it had to be official or sanctioned by management. Chances are only a few devs are involved with the core engine. Most employees are silo’ed into their own stuff, guys doing card design, balance, art, marketing etc.
This has nothing to do with generating revenue, this is about someone putting little side projects themselves for themselves. It’s like how you can have a complex system that a developer makes things hard to understand so if they were ever to leave (not voluntarily) updating the code base would be very expensive.