Query selectors likely came from jQuery's Sizzle engine, but most of the jQuery APIs, all methods, were never adopted. The best I can think of that did get adopted is closest which uses a query selector to find a matching ancestor node.

The reason why most of the jQuery approach is not adopted is because it is so incredibly slow. First you have to consider that query selectors, at their best performance (Google Chrome), are about 460x slow than the old DOM methods. All the jQuery approaches would be slowness that multiplies on top of the already slow query selectors. In Firefox query selectors are about 10,000x to 250,000x slower than the standard DOM methods.

From a standards perspective there is no incentive to go down that path as it cripples the interface it describes.