honestly? ease of use. I like Unsloth too, but Newelle is really an easy solution if you just want to use LLMs on you own hardware (or use inference providers) that requires practically no knowledge at all - it is focused on providing something to use LLMs without anything else interfering.
Unsloth does well too, but if i hadn't learnt as much as i already did when i started using it, i would probably have been overwhelmed (outside of it crashing pathetically when following symlinks for local model selection - you can define these directories, but the quick selection then just makes it crash)