Because you are completely unknown and PayPal has a very high fraud rate.
If you're serious about buying bitcoins, I suggest you fund an account at mtgox.com and then put in an order.
Are you able to fund a account via paypal on mtgox.com? I am paypal verified and I can understand people worried about fraud.
Paypal recently shut down the account (and froze assets of) the person who ran the most used Paypal->BTC service claiming selling "ecurrency" is a ToS violation. It's now more than just the high fraud rate. For that reason (at least), Mt Gox will not accept Paypal. You can, however, use LibertyReserve, which is very similar and I think charges slightly lower fees.
https://mtgox.com/users/addFunds
