Your map shows a discomfiting concentration of large impact sites in North America, east of the Mississippi, moreso than any other place on Earth.
Maybe because the searchers look hardest where they have to travel leastest. Or, maybe it’s just that the searchers prefer the cheaper, decent hotels and lodgings in that area.
The old earth folks would say that that is because the surface of the east is geologically older than the west - i.e., the Appalachian are older than the Rockies, with the Canadian shield even older. In Europe, the Alps would be younger, with the Jura older, so you'd be more likely to find impact sites the further you moved north.
probably biased that way due to political-economic-educational issues in much of the world , (not w.europe, but the rest).