The real underlying problem that people continue to overlook in discussing this topic is that this is not a real pro sport. When an athlete's pay can come from one of a thousand different sources rather than primarily from one centralized source then it's simply a collection of loosely affiliated freelancers. There's money in it yet it's not at all run like a real pro league or tour where athletes and agents are organized to have a seat at the table to have a credible say in where the money goes and how their likeness will be used for promotional purposes plus competitive expectations.
Nothing is stopping anyone from showing up with Ford, Dole, Cheerios as the prominent logo on their kit. It's certainly allowed. In fact, there was a Mazda TC many moons ago. It's just that those types of brands aren't convinced that they'll get decent ROI from the brand exposure to be gained. Our sport remains an ever-shrinking slice of the sports pie in terms of public awareness and interest and that's precisely because it's essentially left up to NGBs like USATF, USOPC, IAAF, and IOPC and as a rule innovation doesn't happen there (see also: four major domestic meets held in the same, out-of-the-way location.)