Interesting observation ....because companies like PayPal are not actually trading the bitcoins you buy and sell... they use a internal ledger system to track the ownership of the coins they hold. So those transactions are not done on the Blockchain and no miners fees are paid to the miners.

This can actually be seen as some unplanned attack on Bitcoin, if they operate like this for a long time. (The PayPal CEO said, their business model might change in the future, but we will have to wait and see if that will happen or not)