why
Sights on a firearm are a sort of personal thing, what one guy likes, prefers or can see, another may not. And those preferences can change as ones eyes age over time. I have never cared for Glock factory sights, even when my eyes were young there was just not enough daylight in the sight picture to set the front post off enough to satisfy me. Either the rear notch needed to be wider, or the front post needs to be narrower.....to suit me. Plus, I had two occasions where the plastic Glock front sight deformed under an impact (stuff happens) or the rear sight drifted badly in its notch. The Glock pistol is tough, but their sights almost seem as if they are disposable and made to be replaced.
Though I recognize the advantages of night sights on a defensive pistol, for a hunting or competition rig, the nature of their construction (the dark perimeter sight body, translucent ring and tritium vial) add up to a very busy front sight (for me) and I prefer (or at least used to) plain black on black sights for range and for field. At age 65 my eyes have now slipped enough that black/black is not such a good arrangement, and Big Dots, fiber optics and red dots ( and shooting glasses) are in my future.
There are lots of Glock sight options. Though I am leaning towards XS Big Dots (unfortunately), the Sevigny black/black competition steel sights offer a narrow front blade and sufficiently wide rear notch to be easily seen and are very popular.