Most sports have a salary cap to prevent being able to buy your way to success. They recognize that having more money than your opponent gives you an unfair advantage and destroys competition.
Prepping for 3+ months is definitely not the baseline. I'd really need some convincing that you're getting any real incremental benefit past a week of interview prep. There's not that much ground to really cover and at some point you're just solving different versions of the same problems over and over again.
"Stealing an idea" has been a phrase for far longer than that though. Stealing as a metaphor for intangible objects isn't a creation of the media companies.
It's a way to convey tone through text. Sometimes the same comment can be taken in either a rude or a helping way, and prefacing it with "I don't mean to be rude" is a way of saying "please take this in the helping way."
When talking in person you can infer this through how they say it, but in anonymous text on the internet the disclaimer is helpful.