Ask HN: Why do people post only their slidedecks?

Is it just me, or are most slide decks completely useless without the speaker talking over them. Especially the ones with random lol cats.

Most of the time these slides are not provided with any context, or are random code bits in languages that the reader might not be familiar with.

The rare times when a slide deck is complete and useful, I'm left wondering why it's not just a blog post.

The tools for recording a complete presentation are there, and if you have a macbook, you need nothing else.

Is this a lack of knowledge of how to do this? Should someone write up a howto?