Though the value of bitcoin at the current exchange rate multiplied by the ~11.3 million BTC issued to-day equals some number a little over $1 billion, that is not what the cost would be to acquire "a substantial share". Nobody knows where the exchange rate would end up if another round of heavy buying were to be attempted.
But what benefit do you see they would gain from buying lots of coins?
I dont see much benefit other than frontrunning a substantial worldwide wealth transfer and amassing their peice of the pie while prices are still relatively cheap. That is all anyone can do.