Internet searching will turn up extensive analysis in 2015 when the split was announced, but a simplified view is that there were few synergies between the two businesses, independence would allow better business opportunities (e.g.,
ebay could shop around for payment services, and PayPal could pursue new merchant partners that could be viewed as competing with
ebay), and shareholders wanted to separate the P&Ls so that costs or losses of one business would not drag down the other (e.g., an investor seeking the returns expected of a financial services business would not see that profit margin shrunk by the costs of a merchant or auction business).