Most of them probably did, because it was generally difficult to jailbreak the phone and there wasn't much reason to do so unless you were a hobbyist. App piracy was definitely a thing though, and I bet there were some people who did it because a friend told them they can get free apps, only to end up installing stuff that made the phone very buggy (which was definitely easy to do).

It's easy to say "well that's just their own fault if they installed something bad," but I don't think Apple really cares to argue with their customers over whose fault something technically was. Apple just wants their customers to have phones that are working well.