The world isn't that binary. No one is suggesting you hire a bunch of people who don't care at all about solving actual problems and who would just screw around all day messing with whatever shiny object caught their eye.
The discussion is whether someone who is just in it "for the paycheck" will be able to solve those business problems as effectively as someone who has a deeper interest in technology for technology's sake. By itself, that's obviously not enough signal to say one way or the other. There certainly are extremely valuable people who don't code outside of work, follow new language and tool discussions online, etc. I think it's equally obvious though that such an interest is a positive signal. If you told me nothing else about two potential hires except person A writes Java at work and has no interest in the field beyond that, and person B writes Java at work, but has a Github page full of utilities she wrote in Go, Lisp, Haskell, whatever, I'd bet a small amount that person B is probably better at solving technical problems. You can't say that for sure, and any of the myriad other factors that actually do matter could break the other way and make person A the better hire for an actual business, but outside interest is a positively correlated trait.
The discussion is whether someone who is just in it "for the paycheck" will be able to solve those business problems as effectively as someone who has a deeper interest in technology for technology's sake. By itself, that's obviously not enough signal to say one way or the other. There certainly are extremely valuable people who don't code outside of work, follow new language and tool discussions online, etc. I think it's equally obvious though that such an interest is a positive signal. If you told me nothing else about two potential hires except person A writes Java at work and has no interest in the field beyond that, and person B writes Java at work, but has a Github page full of utilities she wrote in Go, Lisp, Haskell, whatever, I'd bet a small amount that person B is probably better at solving technical problems. You can't say that for sure, and any of the myriad other factors that actually do matter could break the other way and make person A the better hire for an actual business, but outside interest is a positively correlated trait.