Because especially on mobile, screen space is insanely valuable, and if you want to show new information from the new area the map has been moved to you often need to remove "stale" information.
Sure, but it could just as easily be a button to clear this information explicitly or it could just be hidden, but not deleted.
it wouldn't, which is why the complaint in these tweets ("drag the map even a pixel? it erases all your results and closes the infobox you were looking at") is, in fact, not something that happens.