I know I'm a little a late to this question, but wanted to offer my input. I think the answer to this might be two fold. One is that they always need to be invested in something, where as most of using on here trying day trading are mostly in cash over night, except for the swing traders I guess. But they couldn't be sitting in cash over night or even for days at a time.
The second thought that comes to mind in big lot orders might move the price too much, too much in and out, and hence there might not be any patterns to look for.
The big boys simply cannot do what the little boys do. Its like if for example you need to get from one coast of the country to the other. If you have to take a football team, you gotta rent a bus. But if you're gonna solo, it makes much more sense to take your car. In no way could you move an entire team with cars, it would be hugely ineffecient.
I think I read somewhere that HFT firms make trades in small sizes of just several hundred shares, but hunderds of times a day and with tons of different shares. The key though seems to be that if they traded huge lot sizes, the price might move too much and their system wouldn't work.
Anyway... so I think that big institution simply cannot use TA because of their huge size.
