From the introduction:
[The Wayfinder Bestiary] contains one hundred fifty-five creatures, taken from Wayfinder (Issue 1 - Summer 2009) through Wayfinder (Issue 15 - May 2016), contributed by 75 authors, illustrated by 47 artists, and reviewed and edited by our 10 editors[...]
Among that illustrious group, we have current Paizo employees, RPG Superstar winners and runners-up, and a large number of authors and artists who have gone on to be accomplished contributors to both Paizo products and third-party products. It is an impressive alumni, all of whom contributed their amazing talents, and highly valued time... for free.