Because his optimization is
at the expense of all other considerations. He even admits to being pleasantly surprised that his glop
tastes good. That means he'd have consumed it even if it didn't — taste is secondary to convenience.
He's taking what we currently believe to be true about the human body's nutritional requirements, dumping that into a blender all chemistry-set-style (it even has oligosaccharides!), and calling it good, because he thinks eating like a human takes too much time and effort.
Maybe it will work out for him. I'm certainly interested to see what happens. But if what happens turns out to be some previously unknown (because everyone else has been busy eating at least some actual food) analogue of scurvy or something, I'm not going to be the least bit surprised. I'll probably even have nontrivial schadenfreude.
Simply, we do not know enough about nutrition at this point to be making this kind of optimization. It's therefore premature.
(Edited)