Another valid "pistol caliber rifle" reason is to be able to get some short range rifle practice in at indoor ranges that allow pistol caliber rifles.
A rifle is easier to hit varmints with than a pistol[for me anyway]. I like having something that is good at the intermediate range, but peters out faster than a deer cartridge. Shotgun slugs fit into that category, but a pistol carbine has a lot less recoil by comparison. Shot some custom 410 slugs that were close, but still more recoil than a pistol carbine.
Being able to get a carbine chambered for 9mm[or whatever] also allows single bulk buys for plinking. [Well, once upon a time....and maybe again one day
Beretta CX4 storm(9mm, .40, .45) MSRP ~900 bux
Just Right Carbines(9mm, ???) about 750....never seen one in the wild
Thureon defense carbine(9mm, ???) price????
Caracal is supposed to be introducing a 9mm carbine this year, but that may be delayed by their re-working the pistol line in their recall.
And a variety of AR's and AR conversions. Never looked into those much.