People choose to carry guns in fanny packs for comfort, concealment, and versatility. Fanny packs can be a more comfortable option than traditional IWB carry, especially for individuals with active lifestyles (like runners or hikers), those who wear athletic clothing without belts, or people with certain medical conditions that make inside the waistband carry uncomfortable. They also offer excellent concealment, as they don't print as easily as some IWB holsters, and modern fanny pack designs often blend in with everyday casual wear, reducing the likelihood of drawing unwanted attention.
Additionally, purpose-built concealed carry fanny packs often include dedicated compartments and retention straps to secure the firearm, making them a practical choice for those who want to carry a handgun, spare magazines, medical gear and other EDC items in a single, discreet package.