If that zombie startup gives you freedom and a good salary, why shut it down? This is not for bootstrappers or those who pursue life-style businesses, it's for VC backed startups.
It's easy for founders to get stuck in the short-term thinking of "how do I keep my startup alive" and, after months or years of this, end up with a business that isn't going to grow and they don't enjoy or feel passionate about running. I believe this is what Aaron means when he talks about "Zombie startups". It's a pretty common state for startups to get into.
In those situations, it's better to shut it down and move onto something else then stay working on it simply because of momentum. Every year of your life is a huge opportunity cost.
Life can change. That 'hot start-up' that morphed into something that employs you and a bunch of others might be less than what you and your investors hoped for but still substantially more than nothing.
Sucks to be them if it takes off then. After all, your chances of success on the second time around are substantially larger than the first. But then again, you'll also be a much harder case to take advantage off so that would rule out quite a few investors up front. And accelerators too, for that matter.