Seems like .40 S&W is the least popular of the 3 big semi-auto cartridges for starters, and I've read quite a few reports of the .40 Shield being somewhat uncomfortable to shoot, so I'm sure that scares people off as well.
The 40 isn't uncomfortable to shoot if you can handle the recoil.I've shot it 1 handed and it didn't feel uncomfortable doing so. I thought the same when I got the 40,ammo would be easy to find,but I am finding out that where I buy mine at,they seem to run out fast. Last time I bought 200 rounds.I usually only shoot 100 rounds each visit to the range since time is always an issue.
I did see a 9 used for $329 with 4 mags. I have considered buying it so I have a 9 to carry since my g/f doesn't allow me to carry hers.