They only show the good part of 90s UIs, the standardized part. They don't show the part where every installer wanted to look unique, weird ICQ clients.
I don't do much with Windows nowadays, but I do touch it from time to time and I don't think much has changed in this regard. Off the top of my head: driver installers for Intel, Nvidia, and Brother printers all look unique. Same with the installers for Firefox, Chrome, etc. The MSI format has brought some standardization, but it's a fairly rigid framework that leads projects to building their own installers.
