Why do companies already register their ships in Panama or hide their money in the Cayman islands? (Other havens are available)
Because these countries have decided they would rather have the income than agree that what they are doing is somewhere between morally dubious and completely ammoral. It is easy to point the finger though, some of these places probably don't have many other ways of making money...
It's actually quite simple: if you want to do business with the G7 countries - with close to 40% of the world economy [1] - you follow their rules.
While 60% is a lot, it's a much different blend of markets to work with - hundreds of other countries, legislations, etc. - and it would be a much larger effort to cover.
So: wether I like it or not the truth is: if the G7 countries agree on something, other countries will follow.
[0] https://www.reuters.com/article/us-swiss-secrecy-idUSKCN1MF1... [1] https://www.nationmaster.com/country-info/groups/Group-of-7-...