Because PayPal is seeking to also sue people whose names they do not yet know:
6. eBay and PayPal (collectively “Plaintiffs”) are ignorant of the true names and capacities, whether individual, corporate or otherwise, of defendants named herein as Does 1 through 50 and Plaintiffs sue said defendants by their fictitious names. Plaintiffs will seek leave to amend this complaint to assert allegations against the Doe defendants when their true involvement in these matters and capacities are ascertained.
In other words, PayPal employees that PayPal alleges that the former employees recruited to Google.
As I understand it, this is very standard lawsuit boiler plate, such that if they later realize there is another party involved, they can just tell the court, "so-and-so is Doe 1," allowing them to very rapidly fold in new parties without refiling the suit.
I realise "Doe" is "John Doe" - a pseudonym for an unknown person. But I can't see why they are included in the suit (all 50 of them).