Form follows function.
Those who appreciate the Glock for its reliability, durability, capacity, and shootability don't mind the aesthetics, and some even grow to like them.
The Glock is simple. It is the AK of the pistol world. The AK isn't a beautiful weapon either, but it is favored for its simplicity and its reliability under adverse conditions--just like the Glock. And you don't have to be an 11-year old son of a goat farmer in some 3rd world African crap hole to understand the advantages that come with this simplicity either. Few pistols, if any, are as easy to detail strip as a Glock. The Glock has about 34 parts, total. Many of these are interchangeable. None are hand-fitted. This also makes the Glock modular. A Glock 22 upper slides right on to a Glock 17 frame. Magazines between Glocks of the same cartridge are often interchangeable. A Glock 19 can accept not only the 15 round magazines it comes with, but the standard 17 round magazines of the larger Glock 17, or the 33 round magazines for the Glock 18 machine pistol. Slide a Glock 23 upper on a Glock 19 frame, and it goes from 9mm to .40 just like that. With very little training and nothing more than a pin punch, the user can repair or replace anything that can break or go wrong with a Glock.
As much as people complain about the grip angle of the Glock, it does help to control muzzle flip. So does its low bore axis. Compare how low the Glock sits in the hand next to an HK, a SIG, or even a 1911. That gives the pistol less leverage and helps minimize muzzle flip. The Glock doesn't have a target trigger, but it is very good as a combat trigger--consistent, relatively light, and with a very short, crisp reset that helps get follow up shots out as quickly as possible. The Glock also has a very good magazine capacity, a good selection of aftermarket parts and accessories, which again, can be installed by the user without sending the pistol to the company or a specialized builder.
They aren't shiny. Their lines aren't graceful. But they are working guns that can be depended on. They get the job done. And they don't cost an arm and a leg in the process.
I've owned and shot many of the Glock's competitors on the market--SIG, HK, 1911s, Berettas--and I respect many of them. But as I've said before, when the chips are down, I know I can depend on my Glock. And that is simply beautiful to me.