Because it is already priced in the market due to insider trading.
Also the price will go down a lot instead due to paypal users selling BC.
Who said paypal will let sell btc and not only buy them?
For example Payza already supports btc but only for withdrawing to btc, so you can only buy them not sell and the price is higher than in exchanges
I'm sure it will not be useful for trading but it would be still another service which supports the currency and should make it more valuable