My theory is that now that there are people who do nothing except design and tweak the user interface, they can't ever be "done" or else they risk people realizing how wasteful it is to have that job position and lose their job. Most of the time, once a UI is done and works well, it's best to leave it alone with the required minimal changes that need to be done be assigned instead to the general project maintainers, not specialized "UX" designers. They might actually think they're useful, like most people want to believe, so they'll come up with things to justify their employment. It's easy for them to set up and game a "study" to justify whatever change it is they want to make to the UI in order to keep busy and keep their job. The more drastic the change is, the more work it is, the more they can argue the merits of keeping their pointless job going, and the more controversy and fluff they can inflate their head with to self-justify their own importance.