Interest in fleeting cosmetics lasts until the next one comes along, as you so poignently pointed out- there’s tons of cosmetic hearths.
I still use my Hellscream’s tabard as a teleport. I wouldn’t exactly call teleports(A permanently useful item) something with a shelf life. As long as they take you somewhere with achievements, mounts and toys to grind for achievement-climbers, they are useful.
Far moreso than a cosmetic you’ll use for one whole expansion.