I don't think the developers intend it to suck up so much time. I think they want to make something that's fun.
But I don't think there's anything to the game that malicious developers don't already know.
I think, insofar as it's fair to call Factorio addictive, it's because there's a constant feeling of "just one more thing" (or "just one more game"). There's is constant and continuous frontier of optimization opportunities. But, at the same time, there's also effort/delay in getting the rewards of the effort. -- I think that feedback loop is what people loved about the 2012 XCom Enemy Unknown.
I think it's possible to play in a healthy way. But, I guess if the feeling of "my factory isn't good" and "I suck" drives the behaviour, then that'd be unhealthy.
You always have a next step, a next upgrade to look forward to. It's an uninterrupted treadmill from building your first mine to building you hundredth mega-factory. That's how even quasi non-games like Cookie Clicker can become addictive. It's effectively a Skinner's box.
Gameplay-wise Factorio is a lot more interesting that Cookie Clicker of course.
It's an uninterrupted treadmill cos you just spent 3 hours extra doing seventeen other things and realise you still haven't actually "fixed the copper" or whatever the heck it was you were meant to be doing :)
