[greenyouse]

This. Do you currently use Plan 9 for your operating system at home?

By not making the operating system abstractions similar to other existing operating systems all popular applications had to be rewritten for Plan 9. There was a network effect of existing apps that worked well enough and developers were already familiar with the existing systems which made it hard for users to switch over.Plan 9 was a better operating system technically but it didn't have the utility that existing operating systems already provided to users.

Non-computer people would also probably just use whatever OS the computer they bought had. Using something outside of MacOS or Windows was not normal for a non-technical person in the mid 90s.