I believe this is because many people will mix it with fruit, milk, etc., all of which add calories. This allows for flavor-enrichment without straying too far from that 500 calorie number.
Do they no longer send a black “Let’s Get Started…” booklet with first orders? I found the booklet to have the easiest instructions which is part of why I asked about it being made available digitally.
I would still like to see the 5:1 ratio instruction addressed though because, other than what I observed about that being the post-mixing ratio, I have not read an explanation that makes it clear/usable for me.