[XCSme]

They are good at branding/marketing. They have a big team of awesome people (90ppl): https://posthog.com/people

They write a lot of blog posts, which usually tend to go viral on HN.

At the moment they provide a generous free tier too, so many people can get started without paying anything.

They also open-source most of their code: https://github.com/posthog

They raised a lot of money ~$39M

So, I would say that compared to other companies, they got more popular because of:

   * modern marketing tactics
   * huge funding
   * still in growing phase, so they are focused on growth more than profits (phase in which most companies are at their best, as they try to give more than they take)
   * newer product
   * good timing (a lot of people are switching away from GA, which had a huge monopoly over web analytics).