seems like the engineers were allowed into the decision room
cat dict.txt | rg "ium$" | uniq | sed -z "s/\n/, /g"
Who knows? Perhaps they thought it would be spelled more similarly to aluminium, ammonium, auditorium, calcium, compendium, cranium, delirium, emporium, encomium, equilibrium, eulogium, exordium, geranium, gymnasium, medium, millennium, odium, omnium, opium, opprobrium, pandemonium, potassium, premium, radium, sodium, tedium, uranium...