Even setting aside the idea of political usefulness and partisan bias (not quite the same, something might be politically useful by discrediting other factions

Even setting aside the idea of political usefulness and partisan bias (not quite the same, something might be politically useful by discrediting other factions within one's own party), the fact that both of these databases are made by americans is in itself a completely sufficient explanation for the main result of this study. Databases made by americans are going to disproportionally contain websites that tend to be linked by american politicians. But, for the record, I don't think it proves much that two databases lead to similar results.