To be fair, that's because it was never a good round. It became popular because it was new, it had less kick than .45 and a lot of agencies had eyes on making it "the LEO round." But 9mm tech has come a LONG way and you have some really hard-hitting 9mm rounds that are easier to put on target.
I'm a sport shooter (USPSA). 40 ruled the roost in Limited for probably 15-20 years, but yeah 9mm is a lot better now. In LimOps I can run 23 at the start, where I can't get that with 40. I now have a $4k race gun that is basically a display piece. Sigh.
Yeah, I’ve just always been prejudiced against .40 from the time I went into the academy. It was crazy to me because all the SWAT officers were running 9mm 140+ grain rounds and just tearing shit up, while line officers were all using .40.
My competition load is running 165g 9s. I only have to make 125,000 power factor, and they shoot really smooth.