paypal offers:
instant transaction
relatively low fees,no fees if sending to merchant.
high security for buyer but usually both parties-trust
ease of use.

id say only limit pp has its strict rules of what can be used for purchasing,and lack of wider coverage,thus 3rd world countries many dont even have access to PP.

while anynimty is a bonus,but that could be argued,since its not much different has having bank account,or getting prepaid card of third party and providing your details,since given current situation its quite hard to buy btc without giving bunch of your personal details to some 3rd party that youd hardly trust.

BTC has its strenghts in different areas,but mainstream purchases isn't one.