I suspect that's a bit like concluding that the internet is dead because nobody says "surfing the web" anymore.
It's more like concluding that the internet is dead because nobody says "internet" anymore. Still, that trend for "blog" is probably more noise than signal considering the trend for "internet":
That's a better example than mine. I was trying to think of something that also sounded silly, since "blog" has always been kind of a dumb-sounding word.
Given the rise in social media, it's unlikely that Google plays the same role that they used to. There's also no reason to think people are putting "blog" in their searches these days either. That would at best be a weak measure of blog readership.
The graph for 'website' looks similar, so I guess anyone here who is a FE dev should look elsewhere.