Names work well because the actual size of a mattress isn't really important to most mattress discussions, nor are the measurements ever 100% accurate because of differences in material or manufacture. If I'm at the shop buying sheets and I remember my queen mattress is roughly ~1.5m wide, is it a 1.37m wide double mattress or a 1.53m wide queen mattress? Using a name placeholder avoids this ambiguity, a queen sheet will always fit a queen bed, within some margin of error, even accounting for differences in material: I imagine foam is more ductile than spring mattresses so might be made a bit bigger to account for this difference.