PayPal limitation is a very big problem to lots of users earning online .
In my opinion I think the cause of the limitations is in two ways, the first is that PayPal check the track records of every country in terms of the fraudulent activities committed by the users in the respective countries if it is very high PayPal will limit or ban account from such countries. Secondly it also the depends on the financial institution regulations or policies of each countries if it will tolerate full operation of PayPal . That is why the limitations differ from country to country, some countries can only receive funds but can't send while some can only send but can't recieve funds.
PayPal is very restrict and I just hope they review their policies on limitation of account.