The first two require a lot more effort in video editing than creating a forum post. Plus, it’s just going to be digested and regurgitated for the masses by people much better at communicating technical information.
Based on what I know about corporations, it's entirely plausible that the folks posting the information don't actually have access to the communication channels you are referring to. I don't even know how I would issue an official communication at my own company if the need ever came up... so you go with what you have.