Because like it or not 5E is the new gold standard of D&D like games.
Because a claim such as "Game A is less complexity than Game B" can easily be misinterpreted as Game A being accessible and friendly, when in actual fact most readers are not likely to appreciate or even register the supposed reduction in complexity.
In a pre-5E world, Pathfinder 2 would likely be heralded as a great step forward compared to both 3E/PF and 4E.
But we don't like in a pre 5E world. In fact, we haven't for five whole years!