Generally, you didn't actually buy a computer for the OS it ran, you bought it for the capabilities it had, which were always best exemplified by the applications that were available. These days, people care a lot more about the OS, but that's mostly down to the fact that these days your OS tends to come with a suite of applications out of the box.
Back in the day, OS1.2/1.3 were fine, but there was nothing about them that you could really sell using pictures in an advert. If anything, seeing the old black/blue/orange/white colour scheme would probably have put people off!
Seeing business software, fancy graphics and music, games, etc. These are what sold systems.
