I'm not an expert, but am former military (and was NOT a paper shuffler....) and 'big' knives made sense for lotsa tasks.
Then basic surival training came about and in some ways debunked the 'need' for a large blade. I've seen other SERE instructors who carried large knives some favored medium sized. ALL got the job done. Personally i've come full-circle, but have added a second smaller blade outta convenience.
What one pro chooses on a given day is more likely about what the mission will require - environment, etc.
I was taught something about perspective once; its important to remember that carpenters build houses, not hammers. No matter how expensive the hammer is, there are some folks who simply cannot put up a even a simple wall never mind setting trusses or putting doors/windows in.
Same goes with 'survival' gear.... not to say an expensive blade may perform certain tasks 'better', if someone doesn't have a good skill level it simply won't matter.
Pro's get bored with things too and if they can generate some small bit of revenue testing/prototyping some gear - more power to 'em. Its not like these guys are getting rich off teaching survival skills.