The answer for the most part is that its a sales pitch.
There are a lot of people that just look at pre-workouts for 'key words' - ingredients that they've heard of or are familiar with, if that makes sense.
That's why there are so many ingredients commonly put into pre-workouts that really need to be used daily for best results. A good example is one that you just mentioned - Epicatechin. I love Epicatechin but you need to use it daily for best results, and at a dosage that's higher than commonly put into pre's anyway.
I think though that also most people don't think of a pre-workout as starting anything regarding muscle building, they view them as just for energy and pumps. I'm not saying that they shouldn't view them the way you're explaining, I just don't think that most do. Plus, most ingredients that trigger anabolism are things that would need to be taken daily.