you would really need a lot of money to do this and would still take a high risk. plus we can profit by selling high and buying low. so why should i care. bitcoin is all about the price lately anyways.
you said it as you know when it is high and when it is low, could you have predicted the bottom and then the current value? i really doubt
their manipulation is to eat fish that think can predict the market, like you and other, and yes they have plenty of bitcoin to manipulate the market, miners alone have in the range of 100k if not more
this estimate can be easily achievement with the big miners farm that worked for all these years, i also believe that some of the big pool can work together to manipulate the price if it is done at their advantage
so either their influence is so small that there is no real price change or it is big enough to profit.