Not OP. But for me, atomic updates, reproducibility, (to some degree) declarative system configuration, increased security, built-in rollback functionality and their consequences; rock solid system even with relatively up to date packages, possibility to enable automatic updates in background without fearing breakage, (quasi) factory reset feature, setting up a new system in just a fraction of the time required otherwise are the primary reasons why I absolutely adore atomic^[1]^ distros.
I prefer referring to the so-called ‘immutable’ distros as atomic distros instead. It’s more descriptive, because the distros aren’t actually ‘immutable’ but instead they’re atomic.