Usually it goes like that: someone made something useful optimised for a specific use-case with certain time (or competence) constraints, within a total lack of decent alternatives. Then people adopt and use it, it becomes the standard. Then people want to do more things with it, and try to build around that thing, or on top of that thing and Frankenstein monsters get born and also become standard.
If you start from scratch you can do a crypto protocol that is both better designed (causes less UX pain and critical bugs) AND performs better on relevant hardware. Also do not forget that performance is easily solved by hardware: Moore's law and then custom hardware extensions are a thing.
Example: Keccak is so much better from the composition perspective, that when used ubiquitously you'd definitely have ubiquitous hardware support. But if everyone continues to use a mishmash of AES and SHA constructions on the pretext of "Keccak" is not as fast, then we'd never move forward. People would continue building over-complicated protocols, bearing subpar performance and keeping the reputation of dark wizardry inaccessible for mere mortals.