Perhaps it's different in Poland, but in the UK, things like words and names can have connotations and expected places of residence. Different names may be associated with different ages, classes, regions, and so forth. Seeing a name, or other word, outside its usual place of residence, often creates amusement (so, for example, there's a well-known sketch in which two WWII RAF pilots (an identity associated with extreme linguistic poshness and a degree of archaicism) speak to one another in a speech-form associated with lower-class youth, and the audience finds the incongruity "funny"). So seeing The Leader of the Free World called "Ronnie" is funny. "Bill" is less extreme, but still amusing. Indeed, it may well be that a major politician wouldn't be allowed to be called 'Bill' or the like in the UK. We did accept "Tony" Blair, but not without some grousing and mockery at first [it may be that he was let off because the way had already been forged by "Tony" Benn.] But when Dave Cameron became PM, his attempts to go by his normal name were robustly rejected - when he told people his name was "Dave", he just became known as David "Call Me Dave" Cameron, and the name became a vehicle for political attacks - unless you're someone like Big Jim Callaghan, there's enerally a feeling that if a politician oes by too colloquial a name, it's because they're pretending to be somethin they're not.
The class connotations attached to most surnames are much weaker, so they rarely produce emotion. Nonetheless, surnames can be associated with particular classes, races, etc, and the fact that many names that are common amonst the public are not common amon politicians is indicative of something.
I meant to footnote my earlier comment: the fact that Johnson is associated with the black community is presumably why it's vastly more common in the US than in the UK or the Commonwealth. It's a common surname here, but it's two or three times as common in the US, apparently.
But the river tripped on her by and by, lapping
as though her heart was brook: Why, why, why! Weh, O weh
I'se so silly to be flowing but I no canna stay!