That’s a good point, I’ve thought about just extending the cool-down before. The reason I don’t do that more often is when I adjust the intensity for the cool-down, it shows the rest of my workout to appear incorrect. I assume TR may not even take that into account, but it still throws me off visually.
I’m pretty sure the graph is just a visual quirk during the ride itself and that they do a Hollywood style “fix it in post.” 