It's not a mistake, they do it on purpose. Most tech companies spin up with free offerings to acquire critical mass, and then pull the rug out from under their users once they feel like they can squeeze money out of them without scaring all of them away.
Social media does it (Reddit, Twitter). Video games do it (COD, yearly releases, DLC). eCommerce does it (Walmart, Amazon). IaaS does it (Heroku).
Don't give them the benefit that it's a 'mistake', it's very intentional. CAC is a metric used by all tech companies and is calculated to build network effects and large user-bases. I find it unethical and borderline fraudulent to build these community pillars and then defile them for profit. We'll be left with absolutely nothing free in life, no town squares and no transfer of information without fees.
Whether you or someone else can afford $10/mo is completely irrelevant.