There ain't a dang thing wrong with the .40 S&W. Just like the .38 special isn't undesirable just because there is a .357 magnum.

The .40 is what many Law Enforcement agencies want. They consider the 10 mm to be too much for the AVERAGE agent to handle well. When they decided they didn't need anything that potent, they reduced the powder and shortened the case. The .40 has ample power for SD or LEO purposes but given a choice, many shooters prefer to step up to a 10mm.

BTW - That .40 'Short and Weak' thing only means something to people that want powerful guns.