I'm not sure why it was made either but I read a magazine article this spring that said . (and I think this was mostly speculation by the author) that in the early days of reloading brass cartridges it was hard to get smokeless powder.
But black powder was easy to find and the larger bore and different twist of the .32 special made it more efficent with black than the 30-30.
Again just speculation.
The 32 Special was was a smokeless powder cartridge but more suitable for reloading with black powder. As gonecountry mentioned, smokeless powder in 1900 was not that readily available.
The 30-30 (30 WCF) rifling is 1-12 and tends to foul the bore badly with blackpowder. The 32 Win Spec. has a twist of 1-16 making it acceptable with either smokeless or black powder.
The 30-30 with a badly worn barrel will still shoot reasonably well; but the 32 Win Spec with an equally worn barrel is inaccurate beyond use.
If a hunter can hit what he shoots at and limits his shots to under 100 yds., the 32 Win Spec will bring down a Moose like it's been doing for a 100 years.
Rod