Well...you're right, there are tons of fashion schools out there for formal training in technique, sewing skills, estimating needed yardage and the like. But there are other ways to pick up the essentials--my own mother taught sewing for decades (having a degree in Home Ec from back in the 40's when such things were common). I learned the basics from just growing up with her then added to whatever skills I have by minoring in costuming in college. I went into college already knowing how to use a sewing machine, set a zipper and things like that.
My point is simply that there are any number of ways to become reasonably proficient in whatever your area may be. First you need to have the desire to know your craft, to understand the realities of what you're doing, not just airy-fairy ideas. I taught theatrical design in a university, gritting my teeth at a fellow professor who always told the students there was no real need for designers to learn the nuts, bolts and how-to's of costume or set construction, insisting that, basically the tech director, carpenters or head of your costume shop would handle those pesky details. Essentially saying that designers design, the hired help did the grunt work, Just--wrong. If a designer doen't know the potential or limitations of their materials how the hell can they know what is or isn't possible? PR has endless examples of designers not understanding how various fabrics respond or how to--I dunno--set a sleeve or hem a skirt.
There are countless wanna-be designers out there, some talented, some not so much. This is a TV show; I strongly suspect that the producers cast contestants with ratings in mind. Hester is an example of that to me. OK, JMO, as they say.