While I understand the desire for a unified Python ecosystem as much as anyone - this kind of pettifogging is not going to convince anyone to switch to Py3.
Consider if the authors of the article had used (for example) Ruby - you probably wouldn't ask why they didn't do it in Python3, so why do you do it if they write it in Python2?
Consider if the authors of the article had used (for example) Ruby - you probably wouldn't ask why they didn't do it in Python3, so why do you do it if they write it in Python2?