This is kind of a revisionist view of software. I think most of the consistency we remember from software past is because skipping the OS tollboxes and doing your own custom UI was hard rather than because most software developers cared about consistency. Yes the OS vendors did, but one doesn't need to go far to find applications that very much did their own thing. "Bubbly" and "goopy" UIs of the sort "Kai's Power Tools" exemplified were all over in the 90's. Everyone's favorite Winamp was famously not using the standard UI toolkits and had a heavily customizable UI. To say nothing of the many software packages that used the standard toolkits only far enough to give you a window that was then filled with some sort of Macromedia or similar UI that was then completely proprietary to the application itself (think encyclopedia and other educational software of the day). Even the OS vendors couldn't help themselves sometimes (looking at you QuickTime 7)

If older software was more consistent, it's only because the OS didn't provide nearly the same degree of customization options that HTML and CSS provide developers today. Not because of some pride in consistency.