Is there a reason?

I'm assuming the primary reason is because of space in the mags and firearms. .40 is prominently used in firearms based on 9mm frames.

When S&W & Wichester got together to design the .40.  they designed it to specificy be a defense round and they made it to always be a hollow point.  Once it became popular and people started reloading it they started to use flat point bullets because they are cheaper than hollow points but keep the same profile.  

Part of the reason was also like Kevin@AR15com_1&2 said, they were using 9mm frames and if they made the profile any longer it wouldnt fit.  They had to use the outside radius that they did (on the bullet contour) to make it feed reliably but they also couldnt go all the way around with the radius in a "round nose" design without being too long.  If they seated the bullet deeper it would screw up the radius and it wouldnt feed again.  Therefor, the hollow points and flat nose's work perfect but the traditional round nose dont work for crap.

If you want a longer explanation I can do that too but this is already too long to read.  

TRIVIA:  The H&K USP 40 was the 1st pistol specificly designed to use the 40S&W.  After the 40 S&W was selling well they came out with a 9mm by downsizing the USP, instead of it being the other way around like everyone else.  S&W has still never designed a pistol for it, they just keep modifying 9mm's to shooot .40.

good question, I dont think its a lenght thing, in 45 the 230 round noise is not much longer, if any than lets say a 200swc. their seems to be enough room for a 210gr. fmj round nose in 40?

The Firing Line, a shooting range and ammo
mfg. here in Port Richey, just purchased 10,000
.40 hollow points. He has developed a .40 round
that works flawlessly in Paraord guns and mags.
The problem he says is all the P-16 mags are
retooled P14 mags and the standerd .40 is just
a little to short in length for use.