"everything was local"
replyThis was the big thing. There were tons of bugs. Not really bugs but vulnerabilities. Nothing a normal user doing normal things would encounter, but subtle ways the program could be broken. But it didn't matter nearly as much, because every computer was an island, and most people didn't try to break their own computer. If something caused a crash, you just learned "don't do that."
Even so, we did have viruses that were spread by sharing floppy disks.
That's a really big part of it - bugs were ways that the program wouldn't do what the user wanted - and often workarounds existed (don't do that, it'll crash).
replyNowadays those bugs still exist but a vast majority of bugs are security issues - things you have to fix because others will exploit them if you don't.