On a globe earth you are on one side of a bump.
The sun is on the other side of the bump.
The light reflection on the water cannot go up the side of the bump over the top and down to your feet.
There might be a short reflection of light but it would not be able to extend all the way to you.
He showed it very well in the video.
Here is a drawing from Dingbat. (I hope she doesn't mind me using it in this thread.) She was using it to explain another aspect but for our purposes just consider the first example.
You can see that the light reflection on the water would not be able to go up and over the bump of the curve and down the other side to the observer's feet.

I don't mind at all, Miser. I'm flattered that you liked my wonderful work of art here well enough to save it

That being said, after watching the video that explains how the sunlight can't go over the curve, and even looking at my above drawing, I don't quite understand why it
wouldn't be able to go over the curve. After all, if you can still see the top part of the sun, can't the top part cast light on the water?


Maybe I misunderstood your point?? I apologize if so.