It's because of all the different interpretations of "lift intensely, eat appropriately" swirling around. On the internet you have a million different opinions on what constitutes what, and on top of that you have a bunch of people trying to peddle their own secret methods and programs - there's no money in telling people to lift with high intensity and eat a sensible diet. If you scroll through the pertinent websites or ads on social media, of course if everybody and their mom tell you that they have unlocked the secrets (and, hey, they're ripped!) you will start wondering if maybe there's something beyond "lift and eat". It's human nature.
Truth is, most people's intensity and diet sucks (I'm not excluding myself here, I could've done a lot better a lot of the time), so obviously they hit brick walls in terms of progress and then start wondering if there isn't some arcane knowledge that they could just buy for the low price of $29,99 a month. People don't want simple answer, they want easy fixes.
I've had a number of guys come up to me at the gym, asking me what I did for my pecs or shoulders or my diet because my body changed, theirs didn't. I actually took the time to explain to them that there's nothing to it, other than adherence to good practice. Most of them will be like "well, okay, thanks, I'll think about it", then continue to bench 135 for 3 sets of 8 M W F, as they have been doing for the past 10 years, wondering why their hard work isn't paying off.
Then you have the "perfectionist", the guy who will read every last article on a given topic, without ever applying any of his knowledge.