RubyMine is now free for non-commercial use

I don't understand. Of all offerings from Jetbrains, only Pycharm is free for commercial use. Others have restrictions like RubyMine.

I would be interested to know the story there. It seems like a strange choice to be the only one free for commercial use.

Perhaps it has a dependency with a license that forbids those kind of restrictions?

That's not true: IntelliJ was the first one to come out licensed as Apache 2, and PyCharm (and the python plugin) followed suit. Both of them do have paid versions with more features, but IntelliJ and PyCharm open source builds are still very strong products and unquestionably not "phoning it in" releases

PyCharm lives in the IntelliJ CE repository, both are Apache 2.0 licensed, while the rest of JetBrain's language plugins are proprietary. They are 'unifying' PyCharm and getting rid of the separate PE and CE builds, but the underlying plugins remain developed in the open right there on GitHub.

As far as why only IntelliJ and PyCharm are done this way (excepting additional plugins many developers would end up wanting only coming with a subscription), that's a strategy question you'd have to ask an exec about. If I would hazard a guess, Java, Kotlin, and Python are all pretty big first languages to pick up and have large, active communities. Good products to get people hooked and want to pay to get the extras that aren't available without a subscription.

IntelliJ IDEA Community version is also free for commercial use, it's Apache 2.0 licensed even (mostly).