Why Python 2 and not Python 3?

Short answer is: because Python 3 already benefits from a better, more complete client: aioh2 (https://github.com/decentfox/aioh2) that works with Python's asyncio.

th2c is mostly intended for Tornado backends, trying to keep a similar interface and compatibility with Request / Response objects.

It was initially developed in order to be able to communicate with APNS from a python 2.7 environment.