I wish this wasn't such a commonly shared opinion. Too defeatist, in my view. Craigslist is spartan, sure, but there are less extreme examples such as McMaster-Carr. They've had the same design more or less since 2010 at least and it is usually considered both functional and tastefully current. I think in the early 2000s they had a different design which was fine, and they obviously skipped the whole "web 2.0" era of design.