Bitcoin and paypal are different from each other. Paypal process transactions for example, shopping online will be the best one for this. Paypal is the middleman from consumer between the seller. Bitcoin is a virtual money where we can use in exchange for goods or services.
I really agree with you. Between them is a big difference, and even to raise the question in this form is simply wrong. But apparently people too carried away with the idea of replacing all bitcoin currency and even payment systems. But I think it's a bad idea. Bitcoin is a currency for the network, and no more.