We've learned a lot by creating these per-site blogs for any site which asked for them. However, we at Stack Exchange have not been doing enough to make blogs work - neither for the contributors nor for the communities that are associated with them.
On our network, any site will have generated some amount of valuable content; it's what we’re set up to do. But ours is a platform that promises an engaging community, one that responds. We strive to eliminate those cases wherein someone finds a question they need solved, only to discover that it was posted 4 years prior with no response. This is why we shut down sites in private beta, and even public beta. Blogs aren't Q&A, but the spirit remains the same - a blog with content but no updates is a promise unfulfilled by our network.
Right now, out of the 22 community blogs on the Blog Overflow system, only 10 have posted within this year, only 4 of which were within the past 3 months. 6 more posted something most recently within 2013, and the remaining 6 posted last in 2012. This has caused the image of the blogs on our network, internally and externally, to be viewed as inactive and disused in general, drowning out those few who remain dutifully active.
Much of this is our fault: we never successfully integrated blogging into the normal experience of asking and answering questions. We may someday find a way to do this, but it won’t be tomorrow - and it’s not fair to anyone to keep encouraging participation in a broken system; their efforts would be better served finding ways to share their knowledge on the main sites.
Many thanks to everyone who participated in this experiment thus far - I do believe we’ve all learned something along the way. Existing blogs will continue to be hosted and supported as long as doing so is feasible, but no new ones will be created.