Hypotheses:
We have strong models for how to do a popular blog about progress (Tyler Cowen, Anton Howes, Jason Crawford, etc). We have fewer of those sorts of models for EA.
Progress studies, as it exists, sort of only is blogging, so all intellectual effort is channeled to it. EA encourages people to do lots of other things.
Progress studies is innately better suited for blogging. This seems unlikely to me. But I do believe some subjects (philosophy stands out) are harder to blog about. Related: History seems especially easy to podcast about.
I see them as compliments! I expect blogging encouraged by the prize will on average require less context to read, and will often be done by people who aren’t members of the EA community. I hope that as authors and readers think more about these topics, they will find their way here.