I believe they're discussing that awscli was targeting Python 2.x for the longest time, e.g. https://github.com/aws/aws-cli/blob/0.4.1/setup.py#L48 up through https://github.com/aws/aws-cli/blob/1.19.112/setup.py#L64 from 4 years ago, seemingly cutting over to Py3-only starting with https://github.com/aws/aws-cli/blob/1.20.0/setup.py#L62

I didn't go digging into it, but I'd guess they used the ubiquitous "six" library for backporting unicode functionality, but the point is likely "but why start underwater?!"