It is probably because of the $80M fund (<a href="http:&#x2F;&#x2F;slackhq.com&#x2F;post&#x2F;134878632730&#x2F;launch-platform" rel="nofollow">http:&#x2F;&#x2F;slackhq.com&#x2F;post&#x2F;134878632730&#x2F;launch-platform</a>) Slack set up for developing apps on their platform.