I can assure you I never said the game was going to be steampunky, since I personally am not a fan of steampunk. Maybe it’s just not often done right - what turns me off is the random gears, pipes, etc, randomly slapped onto everything, where often it makes no functional sense.
It is, however, a Victorian era time period, with really more like a smattering of influences, borrowed across colonial to WW1 time periods. Bows had fallen out of common use by then. Of course, we didn’t really exclude bows just because it didn’t fit into our time period - it’s a fictional world and we already don’t strictly follow any real-world chronology. As Zantai said, a big reason I chose to forgo bows was the extra animation and item-art work but I also just didn’t really feel compelled to add them. So, it was a combination of saving time, while also building the fictional world as I wanted it.
I’d just made an ARPG with bows but no guns or crossbows. I wanted GD to feel less high-fantasy / medieval and thought it would be cool to stick with just guns and crossbows, for a change of pace. I think that better fit the type of world I was trying to create.
In terms of variation in ranged weapon feel / mechanics, I think we could have had more of that without bows and bows wouldn’t really add that much to it. We don’t mainly because we just didn’t have the capability to spend time creating different nuanced mechanics for different classes of ranged weapons / the pre-existing system didn’t really support that. You have to keep in mind, GD grew from very humble beginnings. If I’d known from the start that I was going to get all the funding and developers we ended up with, I’d have designed certain aspects of the game differently. Starting our with no funding and just myself and Rhis full-time, I had to plan small.
That said, I still wouldn’t have added bows. 
Maybe we can work on some more varied gun / crossbow mechanics if we do GD2 though.