They wanted a revolver because it fitted the character, that was the look they where after. A classic detective look. They added some other things it to make it look like a future weapon, things that didn't have any apparent purpose other than to make it look big, powerful, a bit unique and like something from the future. They didn't have to explain how this work, what everything was, why there are two triggers and so on. It is a sci-fi looking revolver. If FL would change that, a whole lot of people would wonder why (and also the weapon would no longer be the Blade Runner Blaster).
As I seem to recall, it's actually the other way around: they weren't "shooting for" (pun intended) a "sci-fi looking revolver", but rather a "revolver-looking Sci-Fi gun".
The "bastard child of a hair dyer and a hand vacuum" design that Syd Mead drew for Sir Ridley's "Black Hole-Beam Gun" didn't fit the aesthetic (duh!). Instead, the prop makers were directed to create something with rough lines that aesthetically could remind the viewer of a revolver.
By no means was it necessary for it to actually be (as in in-world "actually") a revolver! Nor, indeed, does it bear any — any! — external feature recognisably belonging to one.
And as you say: they didn't explain how anything works. They didn't need to — after all, it is just a Saturday Night Special dressed up to be unrecognisable, and look cool and futuristic. That's all it was or ever needed to be.
For the filmmakers.
For us though, it's a bit different, innit? In the world of our game, in the hands of our characters, it's a real gun, where all the greeblies suddenly have a real function. And so, we need to rationalise them — preferably in a way that actually doesn't directly contradict what our senses tell us when actually looking at the weapon (wouldn't be the first time, though).