If you want documented evidence that there is a nefarious cadre of organizations hacking phones en masse using high-profile exploits before you’ll believe that out of date phones are something to give a shit about, then you’ll never be “presented with an actual case.”
What you’re describing isn’t the reason why we should care about security. If you don’t care, whatever, but planning for bad things that could happen is just basic preparedness even outside of computing. If a fire started in my apartment and I didn’t have a fire extinguisher I’d be fucked regardless of how likely I think a fire would be.
Okay, then you don’t care. That’s fine. There’s no mass hacking of phones going on, that’s not the risk and whoever told you that it was is stupid.
It’s an individualized problem, which is why it doesn’t make the news and why you’re on your own when companies fail to keep your device up to date. It’s not as sensational as a massive fire so it’s hard to care about.
Anyway, hopefully you’ll never have to worry about being hacked. The odds are in your favour, after all. The issue is when you get unlucky.