Licensing and stewardship at the least. 7 years ago, back when Nokia's coffers were fat and they could afford to fund the original PySide, for some reason they could or would not just buy up Riverbank Computing. That's the (presumably commercially successful) business that develop PyQt and sell licenses and support contracts for it. Architecturally PySide has a few incremental technical advantages, the kind you only get with hindsight and cloning an existing project, but overall it looks and feels pretty much the same and was intended as a compatible work-alike of PyQt.
I've a feeling there is a lesser told story in here somewhere relating to Riverbank. No doubt they had been approached by Nokia back in the day, and possibly also more recently by the Qt Company.
> Initial research into Python bindings for Qt involved speaking with Riverbank Computing, the makers of PyQt. We had several discussions with them to see if it was possible to use PyQt to achieve our goals. Unfortunately, a common agreement could not be found , so in the end we decided to proceed with PySide.
