Let's compare: GP100 (in 357) vs N frame (44 special)
Weight: 40 oz vs 37 oz
Cylinder dia: 1.56 vs 1.71
Length: 9.5 vs 9.6?
Shots: 5 vs 6
Just at a quick look, the N frame would have about 0.15 greater cyl diameter, weigh about the same in 44 special, be about the same length, and offer an extra shot...so what would your REALLY get with a GP100 44 special?
Meanwhile, S&W's last run of 44 specials is still available at Buds - $560-570, nickle or blue. Not sure when production stopped, but that tells me they were NOT big selling guns!
I'm considering buying one of the 44 specials from Buds. A 44 special can do everything I want without the omph I don't need of a 44 Mag. However, they also lack the option of shooting 44 mag, and 44 special ammo costs as much as 44 mag and is harder to get, and frequently isn't loaded to a more appropriate 850 fps range...which is why I'm still CONSIDERING even tho they are N-frames at an excellent price (by today's standards).
The 44 special is an awkward cartridge to market. Less energy than a 357 (and no, I don't think energy means very much in a cartridge, but lots of folks do), less flexibility than a 44 mag, less availability than almost anything...kind of a light 45 acp with more expensive ammo. If I am sitting on the fence, then I suspect a LOT of others never got on the fence, and that is why no one is making them in significant numbers.