Windows 95 was the last release that had serious user testing in controlled environments. (They were also cribbing lots of notes from NeXT, which helped.)
Something fundamentally switched around 1998-2002 in how interface design was viewed and approached. I started my career in software as a design summer intern at a company that made a Windows “groupware” application in 1997. They took pride in following the platform’s guidelines and actually testing their designs with real users being videotaped trying to use it. The company’s UI design department was tiny, but employed both an industrial designer and a cognitive scientist.
Five years later, everybody I met in UI design was a graphic designer who was drawing glossy website mockups in Photoshop. The elder lore of science-based UI design was completely lost when Web 2.0 happened and app designs became vibes-based. Even Apple couldn’t resist the tide. (Indeed Steve Jobs’s return to Apple in 1997 was a major contributor because he had developed a taste for user-hostile skeuomorphism like the brushed metal QuickTime Player.)
Skeumorphism is the opposite of user hostile. Flat design. Now THAT is user hostile.