Qiita has been acquired by game company Ateam 3 years ago. Possibly it works for the company's advertisement. They also selling collaboration SaaS called Qiita Team. I don't see any their cool monetization.

Zenn has been trying to sell paid article for profit. That's not so cool for tech perspective but it's looks good for me if they succeeded. Zenn was operated by single person but it has been acquired by IT(AWS) service company Classmethod very recently. Maybe they also work for the company's advertisement.