I run them on almost every pistol I own. 21 year Officer and a full time instructor.
That’s not to say every dept allows it, but we certainly do. I can’t see any reason not to allow them. It certainly doesn’t do anything to make the pistol less safe, nor does it deactivate any safety features of the gun.
Not promoting one way or the other, but A reason I could see some not wanting it is if the user hasn't trained enough with it to be familiar.
Example: Person gets "New" equipment doesn't take the time to familiarize themselves with it or buy proper gear (mags) to go with it can lead to issues. Proper technique will seat the mag, improper technique has the mag in the well but not fully seated, first shot an flop goes the mag.
My department would allow mag wells as long as the pistol would pass the annual safety inspection. A mag well on most pistols doesn't affect a pistol's safety. I opened for no mag well because I felt I could reload fast enough (I practiced and competed a lot), and a pistol with no mag well is a little easier to conceal. As I had to conceal the pistol all day, every day, ease of concealment won out over a reload being a tiny fraction of a second faster.
Double stack magazines are easier to reload without a mag well than a single stack magazines.
Can't speak for law enforcement, but military is no user repair or modification. We couldn't even restake a spring in a Remington 870, it had to go back to Crane.
Personally, I think a double stack mag has a big enough hole to hit. The top of the mag is small and tapered. My single stacks have a good flare filed into them. For a 1911 race gun I can see the utility in the mag well.
It is true for the military, and more police departments than not.
The military doesn't want PVT. Joe Snuffy doing ANYTHING to his weapon. Because he's probably going to fuck it up if given freedom to start doing stuff to it. Police departments often have the same view of thier officers. The bigger the department, the more they think this way.
The other aspect is litigation. An officer that cares enough to modify his weapon could be portrayed as a "gun nut" who made his weapon more deadly by a defense attorney. Don't laugh, it's happened.
My issue weapon has a bit of a flare, but I am not a fan of adding a mag well to the gun. Some work reasonably well, but most make it harder to pull a stuck mag out. Most make it harder to conceal (for those of us who either have to or want to). Magwell's don't make your reload faster, though they can reduce the number of fumbles a user experiences. They can also increase the number of fumbles, when you don't understand how to use them. They address an exceptionally small part of an exceptionally rare event, and they do so with mixed results, while adding a failure point to the gun. Not worth it, imo.
Frankly, it is mostly an attempt to buy skill. I get it, as we can't all train as much as we would like, but this area just isn't important enough for the drawbacks to be worth it. Now a built in magwell, that address the issues above, can be an advantage, but for the less skilled, it really is probably a wash. This is proven to me on a weekly basis, but ymmv.