Indeed - I remember this situation very clearly. Back when Office 2007 came out, there was no first-party way to create applications like that, and after a year or two, only few third-party libraries that were lacking in quality and polish.
This was the turning point. Clients asked us for it, we tried, but ultimately we decided to ditch the bad libraries and do our own thing - then the clients decided they might as well define their own UI design language if they're paying for UI component development.