I've definitely been on the receiving end of experienced (10+ years) and competent (or, at least, clearly not incompetent) developers solo-developing inscrutable code that their colleagues had to pick up later. In contexts where they contributed code to bigger projects, their code showed more focus on readability.

I'm sure I've inflicted my share of hard-to-understand code too, most likely out of not wanting to spend extra time on some byzantine section of legacy code.