Hollywood Gun-Smarts (??)
This IS a curious convention in movies, isn't it?
I think it began way back in 1972 in "The Godfather" when the young Al Pacino used a heavily-taped .38 snubby for the restaurant scene "hit" on the crooked police captain and the competing mafia dude. The crude grip-tape apparently was there to eliminate fingerprints and enable the shooter (Pacino) to avoid incrimination. At any rate, the film's director, Francis Ford Coppola, was probably trying to be true to Mario Puzo's novel, and Puzo did decent research/homework for it.
On the other hand, since Hollywood is notoriously "stupid" with gun technical issues, I suspect this whole thing has become a copy-cat AND cultural-bias thing, i.e., guns are dirty-evil objects... used only by Criminal Elements and/or our blue-collar lower classes. Hence, the half-assed grip-tape jobs on guns visually reinforce this whole "guns are seedy" impression.
Many movies don't even have a "weapons/technical advisor" listed in the credits, leaving these choices up to the Director. That's like giving Hillary and Dianne Feinstein the authority to re-write the Constitution. I once had a Hollywood "property master" (the guy who provides/inventories things like guns, cars, etc.) friend who got me onto the set (as an ad hoc weapons consultant) of a war movie in production, and I saw first-hand his challenges in trying to bring some semblance of technical authenticity to the movie.
Very few movie Producers/Directors/Writers give two hoots about firearms authenticity issues because they "look down" on those in the "gun-owner sub-culture." A rare exception to this is writer/director Michael Mann (Collateral Damage, Heat, Miami Vice, Manhunter, etc.). If you check out his films' demographic ratings in the Internet Movie Data Base (IMDB) you'll discover a clear "like" by men... with an equal disdain by women. And, if you really want to see Hollywood's ballistic illiteracy/stupidity in action, just check out any "chick flick" (if you can sit through it without puking), or the movies shown on TV's girl-fluff/soap-opera/metrosexual-pretty-boy channels (i.e., Lifetime, Oxygen, etc.).
In the end, this is indicative of the cultural-political-gender biases of the film's makers. And, most of the time, they cast huge shadows.