The ICC is incredibly important, incredibly young and global. Shifting this to europe would not solve the problem.
If the ICC was able to have a contract with a fully sovereign supplier, that would be a whole new can of worms. It would be a matter of time (hours? days?) until a fully sovereign corporation put its profits above its negative impact on people.
More than that, how does an organization funded by a group of nations avoid the budget becoming politicized?
The issue is complex and the silver bullet is hard to find.