Let's say it was a layer, instead of a modal. There is still, more often than not, a mechanism that tracks whether you interact with that layer. In protest, say you don't click to dismiss the layer at all. Is that ever recorded? therein lies the problem.

By no means am I an opponent of collecting metrics. I do think it is a very important process of the software development paradigm, but there is a right way and a wrong way. Too often are we bombarded with the wrong way.