Probably the same reason (or at least somewhat related to) that Google App Engine only supports python 2.7. (<a href="https:&#x2F;&#x2F;cloud.google.com&#x2F;appengine&#x2F;docs&#x2F;python&#x2F;" rel="nofollow">https:&#x2F;&#x2F;cloud.google.com&#x2F;appengine&#x2F;docs&#x2F;python&#x2F;</a>)