I suspect the tooling isn’t quite there yet for desktop use cases.
If I were to try to replicate my current desktop in an immutable model, it would involve a lot of manual labour in scripting or checkpointing every time I installed or configured something, to save a few hours of labour in 2 years time when I get a new drive or do a full install.
The case is easier for defined workload servers and dev environments that are regularly spun up fresh.