Mostly for the convenience of having all my games in one place (or loading the games from external NAND media like a memory card instead of an optical disc, see the OG Xbox, Wii, PSP, Gamecube, PS2, etc...) but also because it's nice to be able to play my emulation library on whatever console I pick up, and also have some cool homebrew apps the system was never originally designed for. Like playing 720p MP4 files of anime from my Wii to a CRT television, or using my Switch as a portable FLAC/MKV playback device on the go. I love the freedoms CFW provides, as well as the QoL improvements over the stock firmware/OS experience.
The stock Switch Horizon OS is the most barebones I've ever seen on a modern home console. It's quite pathetic, truly. Only 2 "themes"? (It's actually more like a light or dark mode, as there's no real theme of anything.) No Netflix? No Streetpass predecessor? No built-in games like the 3DS had? No cameras on the device? The Switch is several steps backwards from the 2/3/DS/i/Lite family and it's really sad to see such a stripped-back system, from both a hardware and a software perspective.