The Perfect Protein Supplement -- Why Not??

The reason escapes me, so I must ask: why not an all-in-one?

Why the separate creatine, whatever-whatever, etc.-etc., instead of
just puttin' 'em all in one big tub of mix?

Not that I can make heads or tails out of all the claims, anyway -- but
I've come across rather few all-in-one protein supplements. The ones I
have come across seem pretty weak on protein-per-serving, or really
pack on the calories. I think a nicely balanced on would be 30-40 g of
protein per serving, at no more than ~210 calories, with creatine or
whatever the hell's supposed to help fuel muscles during the workout
itself, etc. If the thing is so essential, why not just throw it in
the mix!

I love a good meal after working out, but I'm sure I'm loading up
hundreds more calories than protein, so, supplement-skeptic that I am,
I'm going to have to finally get serious about taking these protein
shakes. Still, I've taken these shakes as meal replacements every now
and then, only to be hungry in another hour or two!