I think a lot of this boils down to user-friendly formatting. I was very into having a blogspot humor blog and collecting great artwork, videos, etc. I found more and more that it was just a lot easier to use the pre-existing template of my Facebook page to post and share things that I liked rather than having to copy and paste embed codes and fix the size of the video window, and check the blog then open it back up and do formatting changes.
I think the more professional/magazine style blogs that have a strong umbrella concept are great just as they are, but for more personal small scale blogs, it does become just easier to open up a "business" Facebook account and start blogging.

"The zucchini would bide its time, earning the children's trust, learning the lay of the land. And when the family turned its back... Operation Tossed Salad would begin in earnest."

It's infamously known that IDAHO was named as a hoax by a US politician who claimed it was Native American for "Gem of the Mountains" but later admitted it was a hoax, but by then it had stuck.