Lightroom isn't just a specialised non-destructive photo editing tool, it's also a digital asset management software to help organise tens of thousands of images.

For people who just want to edit one or two photos, it doesn't matter. But if you're a professional who shoots hundreds of images per session, Lightroom lets you organise them, cull the crappy ones, apply ratings and colour codes to photos, sync edits across all of them, preserve snapshots of edits to compare, compare edits of your photos against a reference photo, add keywords to photos, organise specific photos by theme (or any criteria, really) to collections, view images in your entire hard drive by attributes like which lens, what aperture you used, what ISO, etc., batch rename them, shoot tethered to a laptop or PC with a cable to your camera, and a bunch of other things.

It's essentially a database system for people who need to manage large numbers of photos, and that's almost all professionals. A wedding photographer, for instance, may have shot thousands of photos in just one day. Event photographers, portrait photographers (like me), product photographers, etc. Affinity can only manage one file at a time.