Wouldn't he only be lazy if he's not doing anything else more productive instead?

Of course not. It's rather easy to see how one can choose to be lazy and not do hard work while being "productive" doing easier tasks. But this isn't about the dev, it's about the culture.

He gets payed to do a specific job,

Again, stop thinking I'm calling the dev lazy, you're completely missing my point.

and does it the best way possible given the constraints. I don't see how you find lazyness in that.

This is the laziness. The constraints imposed by management to get new features out the door at the expense of making their existing features work better is a hallmark of the current development era.

I'm not even going to respond to the last bit because it's entirely irrelevant to (and completely misunderstands) the point I'm making.