ICC is not a government organization, is an intergovernmental organization. This will make it much harder to convince all the stakeholders and to reuse any work done somewhere else.

Many governments employ millions of people (https://en.wikipedia.org/wiki/List_of_countries_by_public_se...) so for them the costs of having even tens of additional workers (IT, support, etc) to maintain a system will be a lower percentage from the total budget than for an organization with only 800 employees.

Well there are many member countries, the ICC maintains its own infrastructure. Its not like they have to get approval of member states to make technology decisions.