Why?
Because you don't really want to be digesting protein when you're trying to perform big effort. It adds nothing to your performance and if anything will decrease it. Carbs and amino acids before a workout are more beneficial.
However if you're talking about a protein meal, then of course protein a good hour at least before the workout will help - but pre work out (i.e. literally just before working out) you're wasting your time and money. For pre workout calories to be of use to your workout they need to be digested. BCAAs need almost no digestion hence why they are favoured for preworkout.
Taking a shake 30mins before workout is fine - I'm taking about literally before a workout. I personally am more bothered about energy and focus, but still amino acids are important, hence why I include them.
I bet that tastes like absolute rotten death!
It's not the nicest! I've actually bought some orange squash to dilute the taste - it helps... a little.