Why are there so many large transactions on the blockchain? On block explorer you can see a list of the latest bitcoin transactions. I have watched it for a couple of minutes now, and I have already seen about ten transactions in the range of 250+ bitcoins, which translates to millions of US dollars.

Is there a reason that there are so many large transactions on the blockchain?
It's not always possible to tell, but often times it's been shown that large (100's to 1000's of bitcoin) transactions are related to exchanges settling with multiple clients or simply adjusting their cold storage around.  

Exchanges holding coins on behalf of customers who move to take their Bitcoin off the exchange (which many people try to do before hardforks) would have many such transactions.