But they're heavier and more expensive to ship. I doubt it's that hard to make matching lids to spec. The industry makes matching toilet seats separately, after all.
It must have something to do with the material. A thread on Reddit suggests a couple possibilities:[1]
- porcelain in more anti-bacterial than plastic (is that true??)
- a heavy lid offers more sonic insulation of the rather loud hydraulic mechanism (this seems plausible)
Man, I did not plan on getting obsessed with toilet lids today.
Could be because of production reasons. Easier to get it produced in the same place than to coordinate shipping to another place and assembly.