If you get a chance to see how Ilfords plate coating line works you'd understand why it's expensive and I'd guess the Belgian facility's not far different.
Production volumes are so low these are small lines, in Ilford's case taking up the same sort of floor space as their test/pilot coating line which is used for test coatings of film and paper and also things like filters. All emulsions are test coated and checked before final coating on the main coating line. A short glass plate run is relatively labour intensive needing two people one loading the plates the other almost catching at the end of the line. However when glass plates were the norm different coating lines were in use and plates were cut to size after coating in many cases.
Commercial plates are now used because of their high dimensionable stability, their major use is in nuclear research facilities. It's actually slightly ironic that in fact Governments have propped up and helped many emulsion manufactureers, from Ferrania in Italy, Agfa in Germany etc.