But this kind of branding wasn't as prevalent before web apps invaded the desktop. Now the users are pretty much conditioned to expect every app to do its own thing.
This is ahistorical. App branding now doesn’t hold a candle to the late-90’s mania for every app having its own skin engine. App-vs-platform UI deviation is a lot tamer nowadays.
I dunno, I would say the 90s (well, for Windows and MacOS, DOS and the other no-standard-GUI OS’s that were still very much alive in at least the early part of that period are a different story) were pretty much the low point in terms of degree of UI branding for “professional” apps.