Because they didn't sell it, they spun it off. Shareholders got 1 PYPL share for every share of EBAY. EBAY was ~$28 a share and the combined value of both is currently ~$123. An 80% annualized ROI seems like a goldmine to me!

I have not checked the details, but I read it as someone who held a share in Ebay+PayPal prior to PayPal being spun of got an Ebay share + X PayPal shares at the time of the spinoff. I don't think PayPal was bought for $50B, it was valued as that as a separate entity. The PayPal share has doubled in value since the split.