It ends up depending on what rules are allready established in the fictious lore, which renders realism pointless.
Once again, you're totally missing the point. It's not that the rules established even CAN render realism pointless, but rather they're all a FACET of realism. You don't suddenly "lose" realism because of the time travel paradox as displayed in
The Terminator (1984) that I brought up, because it treated it realistically. See that word cropping up again? You don't suddenly "lose" realism because totally fictitious elements such as magic are added to the setting. Realism is a consequence of paying attention to detail, adhering to whatever "rules" may apply to what you work with, and acting accordingly. Changing rules doesn't affect "realism" unless so many are added that they start to contradict each other. For instance,
Terminator 2 AND/OR
Terminator 3. The first film depicted a realistic possibility for time travel including a premise for why a cyborg was necessary and why a soldier from the future couldn't keep his toys. The second film ignored BOTH the crucial premise as well as the realism of the possibility itself by changing the rules in a contradictory fashion. Then YET AGAIN the next film changed it once more, while although it could be argued it somewhat adhered to and reinforced the rules as presented in the 2nd film, it also contradicted those rules and present another entire possibility which was not reinforcing nor reminiscent of the first film, yet conflicted with the concepts as presented in the 2nd. In and of themselves, their cross-continuity contradictions didn't render the entire concept unrealistic. After all, T1 STILL followed its own rules, which made sense.
Take another, wildly different example. Acting. MANY people complain about certain genres of TV shows or films because of the acting present, pointing out how people simply DO NOT behave in the way that the actors... uh... "depict them" to be behaving. This is because those genres NEVER assume that anything is different about the setting as opposed to the real world. They DO assume that the setting and rules are identical to our own. No magical fairies, no future death rays, nothing special or different about these settings. Ergo, they follow the same rules as the real world, so when things are not properly representing what would actually happen- be they fiery explosions when real detonations don't look that way, or be they teens who have the odd tendency to allow each other to speak in full paragraphs one at a time and are always armed and ready with culturally-appropriate quips and puns, or whatever the case may be -then these things ARE being "unrealistic". The reason, as always, is because they contradict the "rules" that are established... this time by reality itself.
Again, "realism" and "real" are not the same thing. Adding or changing a premise does not negate realism in any way. Ignoring realism is the only way to negate realism.
To bring it back to the point of the discussion at all...
Once again, it's done so that you can see what characters are equipped with if they're not using that weapon at that specific moment in time.
This is a MUCH better reason given for an "unrealistic" element than any "because video game" excuse. It's still not realistic, but there's a reason for it. Likewise, take MOST shooters, and notice how damn near every one of the (though not all of them) treats ammunition as something you pick up by walking on it. This is ENTIRELY unrealistic, but it's okay and we accept that, because it would be INCREDIBLY inconvenient if we had to physically location and grab and pick up each and every bullet or cartridge, on top of physically reloading. Some games DO do this, however. But as much as I truly ADORE
Breakdown as a game, I cannot escape the fact that its "pick up everything" is incredibly cumbersome. Somewhat immersive, sure, but ultimately tedious to the extreme.
So when you have a game that has a guy with a gun walking over ammunition and that ammunition automatically being added to his invisible stockpile "inventory" without so much as bending over, calling that "unrealistic" is a PERFECTLY VIABLE criticism. Likewise, pointing out that the convention of "magical ammo collecting boots" gameplay avoids unnecessary tedium by presenting acceptable streamlining of repetitious grind to make the game less boring and more fun is ALSO a perfectly viable point.
It IS unrealistic, but arguably necessary.