I would say the complexity of IEEE-754 is warranted (given the history of the standard), but the issue is those writing languages are typically not aware of numerical computing (it's rarely a course at university), and so do not design their languages with it in mind (or predate IEEE-754). This leads to implementations and ecosystems which do not consider it, and we end up with systems where giving the required control to implement IEEE-754 conflict with other requirements (e.g. security, imagine if you could control rounding mode via the browser).