Jailbreaking used to be as easy as going to a website and clicking "jailbreak".
Yes, there was one family of jailbreaks that worked like that, but you'd still need to hear about that and have some reason to want to do it to your phone, and I suspect a very small portion of iPhone owners did that. It would be a lot worse if Apple were forced to allow anyone to make what are essentially jailbreak app stores like Cydia, then one of the biggest video games ever told all their players to go install that so that the video game company can sell digital items at higher margins.
I'm glad that doesn't work any more. I don't want arbitrary web pages to be able to run code as root on my phone.
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.