Anyways, I'm not saying this excuses the quality of most of these things but imagine how much effort you'd put into a Ted Talk versus how much you'd put into a 30 minute meeting when you may only have a few days notice. Most meeting topics are simply boring, it's work, or someone else's domain of work, shouldn't need a ton of narrative fluff to make it digestible, and honestly most powerpoints I see in work in the last decade or so are adequate enough for their purposes. I just stopped being critical of people's powerpoint and storying telling skills long ago and try to focus on the discussion/content being made and what I need to take away/double click on.
Becoming good takes a lot of hard work, lot of redoing of stuff. Just like becoming good at soccer is more than playing games. Many successful YouTubers have learned it's hard work to make good videos.
Like Penn&Teller said: The only secret of magic is that I’m willing to work harder on it than you think it’s worth.
but you have to practice the right way.
the terrible, long-winded, confusing presentations you've seen were most likely done by somebody that sees a presentations as merely "talking in front of a group" so their practice would be focused on memorizing lines/facts that want to say. they may sound polished, but it's not necessarily going to be good.
in order for your practice to actually help, you need to go through your presentation while maintaining a strong sense of empathy for the audience. you need to fight a constant battle against the 'curse of knowledge' and force yourself to honestly evaluate what you're doing from the perspective as a first-time listener.