I've personally come across this dilemma when hiring people. My own take is that's none of my goddamn business and if the person is the most qualified for the job then it's theirs for the taking.
Some day I'm actually going to try this in an interview.
Interviewer: "Why do you want to work for us?"
Me: "Honestly, I don't want to work for anybody because I have too much other stuff I'd much rather be doing with my time. But I need an income to sustain myself so, if I'm going to work, I want to work here because I think it'll be easy, provide decent benefits, and it's a 20 minute bike ride from my house."
It might be worth trying when you are already have another solid job in the background :) It could be that you've hit the one company that appreciates honesty, but generally I think most don't love it.
I don't think is optimal, either. It's not worth investing in onboarding someone, getting them situated in a team, then having to tell everyone a few months in that the person quit. If that seems like a very likely outcome, it makes sense to avoid it.
My experience is the most impressive people are significantly less likely to quit early. If they where doing a lot of interesting things in their free time they either become engaged with interesting projects at work or put in a solid work week and then go home to have fun with their own projects.
Albert Einstein for example worked for several years as a patent examiner while developing special relativity. Sure his contemporary physicists mostly worked in academia, but teaching is as unrelated to research as everything else yet they still did it.