Remember, MacGyver himself may normally refuse to use guns, but even he's not above firing a steering wheel knob out of a cannon, as long as he made the cannon out of a car muffler with his own hands. This can also be an excuse for the hero to MacGyver up some Bamboo Technology rather than just shooting the bad guy. Pressure to reduce violence with firearms in media in general, or the desire of an anti-gun author to teach us all An Aesop may also play a part.

But most of the time, there's just a Writer on Board who wants to show that a character is moral enough to hate overt tools of violence like guns while glossing over the fact that they're in a show where a lot of violence has to be unloaded on people. Some characters will even take a Heroic Vow against the use of guns. Sometimes there's a specific reason that their distaste is limited to the gun, such as a particular incident from his past or a sense that guns are 'unsportsmanlike' or 'cowardly'. He has no problem whatsoever with other, less efficient (and sometimes, more efficient) means of turning living people into non-living people. But in fiction, the gun-hater's reasons are often different. There are lots of reasons that some people hate guns, but in the real world, these are most often linked to hating the thing that people with guns can easily do, which is turning living people into non-living people.

Rimworld how to equip weapons