Those blogs "don't have it" or "don't advertise it"? Seeing that most blogs are Wordpress or another platform that has RSS baked in by default it seems rare to come across one without a feed, even if you have to dig for it a bit.
The first few times it didn't pick up a feed, I would inspect the page source, and sure enough, no `link` tag in the head for the feed (nor references to "rss" or "atom" or "feed" anywhere in the page).
I don't know what stack they use, but I find this particularly common for company blogs.
That isn't to say any claims that feeds are almost a thing of the past holds any water. There are almost certainly more feeds now than at any point before. The second derivative is probably a flat line, though, which is what I imagine is behind the perception of deathliness. Feed consumption, on the other hand, is almost certainly down—but only if you exclude podcasts.