It's so that you can send the slide deck out and people have the actual presentation when they see the slides.
I hate when I go somewhere and they provided just the slides of a previous talk and the slides have no real information on them, there is no context or explanation as to what the bulleted points are talking about.
Not to say that the talk verbatim in the presentation is a good idea either, but people seem to like giving out what amount to useless slides most of the time in place of a recording of the presentations.
If you were to use something like Presentious (https://presentio.us/) to give your talk, you can capture all of the information presented without reading from your slides. And at the end of your talk, everything can be shared with your audience. For example: https://presentio.us/view/p1tcHs
Thanks for sharing Presentious. It sounds trivial, but producing lightweight presentations synced with audio is quite hard. I like how you can go ahead on audio or slides and then sync them back together.
And very few people watch full-length 45 min. videos of presentations even when they're made. Views drop off after 3-5 mins.
At the risk of being obnoxious, the slide deck should be whatever the presenter feels best supports their presentation in front of the audience. At a conference, that should be the overriding goal of the slides. They shouldn't be designed to provide background/context/explanation for someone who didn't see the presentation or didn't take notes.
It's certainly possible to provide a link to a transcript/speaker notes/etc. and I sometimes do. But it's extra work and expense and, frankly, it's not at the top of my list of things to spend a day post-conference putting together.
I think some slide notes could be created even if it takes some extra time. Some viewers might be there to learn and wants some notes/references while others are there for entertainment. If everyone is forced to take their own notes it might take attention away from the presentation itself.
I find that notes are a natural result of preparing a talk. I write the notes to work out what I plan to say while designing the slides to support the script. The notes are the main way to communicate with people who weren't there or who need a reminder of what was said or to follow up references.
I hate when I go somewhere and they provided just the slides of a previous talk and the slides have no real information on them, there is no context or explanation as to what the bulleted points are talking about.
Not to say that the talk verbatim in the presentation is a good idea either, but people seem to like giving out what amount to useless slides most of the time in place of a recording of the presentations.