Some of the departures are a natural consequence of the burnout that comes with working on the same game for more than a decade, others are because they sense an opportunity to chase their dream project in an industry currently awash in venture capital. And some are because they feel Blizzard has been on the decline over the past three or four years amid layoffs, budget cuts, and a lack of major releases, and that it’s time to move on.
https://www.ign.com/articles/special-report-the-inside-story-of-blizzards-departures-and-a-company-at-a-crossroads