I'd bet the majority of the lightweight "Windows 95 clone" WMs and DEs exist because GNOME and (to a lesser extent) KDE alienated their userbases by trying to be "different" and "next generation" (mostly by poorly cloning OSX and the latest Windows version that nobody liked anyway), so I'd hesitate to say that experimentation should be left to them.
EDIT: Many commercial products suffer from this problem where the existing version is "good enough" and people are happy using it for several hours a day, but the producer needs to convince users to purchase the new version anyway, so they end up adding a lot of pointless, irritating, and even product-breaking changes just to make the new version seem revolutionary and worthy of an upgrade, even if it's actually making the product worse. Many open source devs don't seem to have realized that there is no reason for them to play this game. They don't need to sell anyone a new version in a cardboard box, so there's no conflict of interest here; they can do less work and make their users more happy by keeping things stable and incrementally improving things. Yet, very often, they ape Microsoft, Adobe, and company's spastic thrashing anyway. More ribbons!