As the comments point out, the blog gradually became inactive and eventually Stack Exchange discontinued the entire Blog Overflow system. The second link contains most of the relevant information, but to summarize:
- At the time they did this evaluation, "only the SciFi blog was remotely active." That's across the entire Stack Exchange network.
- Meanwhile, the maintenance overhead was becoming prohibitive.
- Worldbuilding successfully started an external blog on Medium, which is still somewhat active today.
Therefore, they decided that it would be best to stop hosting the blogs themselves, since Blog Overflow's mere existence seemed neither necessary nor sufficient for a successful community blog to exist.
Importantly, Stack Exchange has no objection whatsoever to semi-official external blogs. They have actively encouraged sites to follow in Worldbuilding's footsteps. When they shut down SciFi's blog, they permanently redirected it to an external site with the same content, run by a couple of regular users (which is also somewhat active today). There is nothing stopping Mathematics from starting our own external blog, provided we can maintain a reasonable level of community participation in the long run.