Python 2.6 is not supported by PSF since 2013-10-29.[1]
Python 3.3 reached it's EOL on 2017-09-19. Packages have already started to drop support for it.

It's a burden for developers keep the tests passing for these python versions. And, I believe, for contributors to keep the code backward compatible.

If anyone objects, or really needs to run pywikibot with these versions, please reply to this email or leave a comment on T154771.[2]

[1]: https://docs.python.org/devguide/index.html#branchstatus
[2]: [RfC] Abandon support for Python 2.6 https://phabricator.wikimedia.org/T154771