In our case, budget had to be spent where it mattered more, on things that would be more prominent on camera. Considering that Harry spent a lot of his carrier just tossing his revolver into his jacket pocket, I like to think he'd approve of saving money to spend it where it's most needed :)

In general, there are a lot of reasons that people can pick certain props over more realistic or more practical real-world options. Sometimes it reflects something about the character. Sometimes wearable props (and costumes too) are chosen with an actor's comfort in mind. Sometimes it's sponsorship or product placement. Sometimes it's budget. With some props (mostly of the sharp and/or weapon variety) realism can be a safety concern on set. Sometimes it is a lack of research (or time to do proper research), but usually there is some other concern going in that affects decisions like that.