Decimation is a tried and true method to keep the rank and file troops working and afraid, always has been.
I see it more for public perception, 10% seems miniscule imo to the average person who would see this headline (non tech), and a constant compounding can continue to go unoticed.
Plus if every company does it you can begin to forget which company had/has/is/continuing to lay off... Geniusly evil
rounded down from 9.99% to make it seem smaller than "double digit percentage layoffs"
Total number of employees in PayPal are 29000 from wikipedia, with 2500 being 9% of them squarely. I don't know where you got 9.99%
Was thinking the same for a sec ... No sure if they care that much though