I don't subscribe either but this video explains it:
This is showing expected threat, or xT, which I had not heard of until now. I don’t subscribe to The Athletic, so haven’t been able to read more than a few sentences of this but if anyone does, this article might explain what we are looking at. Or it might not, I don’t know.
Expected threat is the next big football metric, measuring ball progression and how teams and players get the ball gets into dangerous areastheathletic.com