The industry itself is only a few decades old.. it'll take some time before it stabilizes to a point where you can largely do the same thing your entire career.

Also everybody doesn't have to present papers, or speak in seminars, etc. but most older developers who are sought after usually do.

Because the person who writes a lot of blog posts is the person who spends a lot of time marketing themselves but not actually getting shit done. If you think a blog post is proof of knowledge, well wow, you'd be shocked at what academia's peer review process is.

Why is that? Given two candidates, one is actively up on current technology and the other isn't, it can be argued the first one has an edge.