If I had more money I'd definitely maintain way more of a life than I do now while continuing to work on my startup. Granted, I didn't really have much of a life prior anyways (remote job coupled with high expenses), so maybe that makes it easier since I'm used to it.
The timescale might seem crazy, but it's incredible what time does for your ideation and strategy. When I first started, my plan was basically a mid-sized SaaS business. Over the years both internal and external forces evolved that into a methodical blueprint for a company on the order of Magic Leap. Six months in I figured out trying to charge money for the product was probably suicide. Six months after that came the start of a radical shift to a far more ambitious plan that built off the original in a very natural way. Had I artificially constrained myself to a fixed time window, or otherwise quit, I'd have never discovered any of that.
The whole thing is very much like an obsession, something that occupies virtually all of your idle thought. Kind of like a nagging splinter in your mind's eye where you can see precisely what you want, the only challenge being to make it manifest.
Taking a fat paycheck as a software developer and everything that comes with it has always been tempting, especially with hindsight—but I know that the second I do it will be the end of my project. Giving up on that would be unbearable, worse than death—at least until I've seen it through regardless of the outcome.
Melodramatic narrative aside, to answer the OP's question—no, I don't think you must have no life to do a startup, and it's even preferable that you have one. For most people, the reality is just that time or financial constraints conspire to ensure that they don't.