The replacement of EN 10204 by ISO 19474 was proposed some years ago but rejected by the majority of national members. Some reasons for maintaining EN 10204 as far as I remember:
1) EN 10204 is a harmonized standard under the pressure vessel directive. This is given in Annex ZA and is essential for the presumption of conformity of pressure vessel material. To add such an Annex ZA to an ISO-standard was not accepted in the corresponding ISO-committee by several members outside Europe. Theoretically it could be possible to add such an Annex ZA only to the EN-ISO and not to the other local versions, but was not pursued further.
2) EN 10204 is cited in practically all EN-standards for steel materials. Replacing by ISO 10474 need changes in all these standards. Moreover some harmonized construction standards like EN 13445-2 (pressure vessels) or EN 12952-2 (boilers) and a multitude of other standards and guidelines refer to EN 10204 and consequently need to be changed when moving to ISO 10474.
3) EN 10204 is worldwide known and not only in Europe whereas ISO 10474 is practically unknown except some countries like Japan.
4) The scope of both standards is different. EN 10204 applies to metallic products whereas ISO 10474 applies to steel products only.

Thank you for your great explanations.I understood all your points.