Many people don't spend $6 or even $4 on three meals a day. They buy lunch and dinner, both costing around $6 if they eat out or around $3 if they make a packed lunch (more for dinner).
There might be someone somewhere who buys a premium breakfast for $4 a day and then spends $4-6 at lunch and dinner, but those people are a rare exception.
Most people are going to compare it to the meals they actually have now and what they spend. It doesn't become cheaper just because they recommend you have it for breakfast too. Breakfast is dead for the vast majority of the adult population (unless coffee counts?).
> On a separate note if you buy a months supply (don't have to eat it in one month) that is $300 for 28 days (84 meals) it comes to roughly $3.57/meal
That's irrelevant because the issue is getting people into the product who think it is too expensive. Suggesting they spend $300 as a buy in is not only unhelpful but also makes them much less likely to want to try it.
Also that's only $1.50 cheaper per day than the base price. Hardly a saving. Still costs above $10/day. Adding breakfast doesn't save any money, it is just a way to make it seem cheaper than it actually is...