Several reasons for a 1911 in 9mm.

Cheaper ammo.

As we age our hands may suffer. A 1911 in 9mm is easier on the hands and wrists to shoot. Years ago I suffered a neck injury that seriously affected my hands both as to strength and dexterity. Couldn't run a wheel gun and shooting a 45 hurt. Also had trouble maintaining a solid grip. Since I could run a 1911 in my sleep I bought a 1911 in 9mm. 100% familiar and I could hit with it. After neck surgery I sold it but it was my orthopedic gun. BTW I had a HP but couldn't shoot it as well as a 1911. Same situation for older shooters and other people w limited hand strength. FYI older now and my hands and wrists aren't 20 anymore. I have 3 1911s in 9mm in addition to several in 45 ACP.

BHP is a great pistol but not everyone likes them. While I would love a Novak BHP the trigger is never going to be a 1911 trigger. While it will be a sad day before I sell my BHP it will go before my last 1911 goes.

Why do we have more than 1 type semi auto pistol? Because people want them. Same is true for cartridge choice.

Because my Robar modified Glock 19 doesn't work as well FOR ME as a 1911. That's for me. Your situation may differ. Glocks are good handguns but not MY 1st choice.

Practice w a 1911 in 9mm transfers to a 1911 in 45ACP. Cheaper ammo can equal more practice. Easier on the hands can equal more practice. More practice done right = better shooting.

What if I work at a PD that allows my choice of firearms as long as chambered in 9mm?

Comparable to a 38 Super although not identical ballistics. Very limited ammo choice in Super. Tons of choices in 9mm.

I'm sure there are more reasons but folks buying them is a big reason.

You could just buy a BHP but I have multiple 1911s, multiple revolvers and multiple 9mm handguns of various makes and models including a BHP and a Glock 19. In reality all I need is a 22 for cheap practice and fun, a J frame for concealed carry and a big bore revolver for a field / hunting handgun. If I really had to I could do it all w a single 4 inch barrel 629 revolver. I could use lite 44 Spec for plinking, heavy Spec for carry and full house mag for field use. And yes I have carried a 629 concealed under normal clothes wo getting made even in a room full of gun toaters who were saying it couldnt be done. I could get by w a 22 rifle and either a 308 or a 30-06 If I had to do so. Where is the fun in that?