Vlog just looks stupid.
Blog makes sense because we often use bl as a cluster (black, blue, bloke), but we don’t use vl.
Blog comes from weblog, and if the videos are on the web and they’re a log, it’s still a blog.
There is some purpose in using the term vlog, because it immediately differentiates itself from the idea that your media is text.
I suppose vlog never caught on because it sounds weird and it’s really hard to consistently make videos.
Perhaps when blog was first expanding it also sounded weird. Same with email and ebooks.
“Words mean how they’re used.”