largely yes. that and dust (which obscures things), and also priorities - the kinds of surveys that provide data for these kinds of map are typically hoping to

largely yes. that and dust (which obscures things), and also priorities - the kinds of surveys that provide data for these kinds of map are typically hoping to increase our knowledge of cosmology / large scale structure / galaxy evolution, which means that they avoid looking at the milky way because (for the reasons given) you're going to see more nearby "clutter".