The sales of the competition absolutely do matter if they make yours look bad in comparison. That being said, I don't think MS ever said anything about the competition at all back when they stopped publishing those numbers in 2015. IIRC Their official explanation was that sales were no longer their "primary metric of success" and thus not worth showing off.
Not that anyone believed them, of course. They had absolutely no problem publishing sales numbers when Xbox 360 was doing as well or better than PS3, and they were giving constant sales updates on Xbox One (which they predicted would
sell up to a billion units) in the first two years after launch. They only stopped when it became clear that Sony was gonna be leaving them in the dust that gen.