Reliable and buggy can go together - after all, nobody left their computer running for days on end back then, so you almost always had a "fresh slate" when starting up. And since programs would crash, you were more trained to save things.

The other major aspect was that pre-internet, security was simply not an issue at all; since each machine was local and self-contained there wasn't "elite hax0rs" breaking into your box; the most there was were floppy-copied viruses.