Ask HN: Why can't I buy bitcoins with a credit card?

As far as I understand, paying with Paypal or credit card is nearly impossible over the bitcoins exchange currently. Why is it so ? For Paypal, I read somewhere that it is because of the chargebacks that paypal allows to the clients. This would make possible for anyone to buy bitcoins, and ask for a chargeback to get their money back, while they still received the bitcoins. Why do Paypal don’t check the blockchain in any way to check that a bitcoin transaction between a merchant and the client has taken place ?

Do Paypal plan to make such a service soon in the future ? Maybe by recording the merchant wallet address as well as the client’s address? This way, Paypal would be able to check for the bitcoins transactions (using said blockchain, as in http://www.blockchain.info ) and then allow or disallow the chargeback to happen.

Do you know why the credit card payments such as Visa, Mastercard, are not used by merchant to sell bitcoins ? Is that because this chargeback issue is in the way, same as Paypal ? Also, do you know if any bank, in the future, has some offering in the works regarding bitcoin payments with credit cards over the internet?