I imagine its wide use is residual, due to how prevalent jQuery was in the past. It is hard to describe how much of a godsend it was back when client-side coding meant dealing with quirks of major browsers and their different versions. It became absolutely dominant in an era right before the explosion of JavaScript libraries that we're still dealing with. Calling it a "big failure of the past" is nonsensical - it solved a very real problem in a very elegant way, and it was a must have for any modern (then) developer. It's no longer nearly as relevant because the browsers by and large addressed the underlying problem, but it does not surprise me that it is still entrenched in many a codebase.