In the article, it says they use Heroku for work and hobby projects. I imagine, like many developers with projects on the side, they try out new tech or platforms on the side and advocate for it at work. In this case, I imagine they used Heroku for hobby projects because it was free and brought it to work (where they could switch seamlessly to a paid tier when usage demanded it) because they liked the platform. On Heroku's side of the fence, I would consider this to be a marketing strategy known as a "loss leader". It's fine for Heroku to take that away, but it's also fine for people to be driven away when the marketing strategy that lured them in is abolished.

I can want free shit. If you offer it, I can use it. If you stop offering it, I can leave and look for more free shit. I can also help other people who want free shit to find it. I can write about it, and you can downvote it if you don't like it. The end.