> What does a country like Malta, Cyprus or Monaco honestly have to lose by being a tax haven?
Simplisticly speaking, they only gain from being tax havens. Point is that everyone else looses. Taxing is a zero-sum situation where if you pay taxes in one place, you don't pay them somewhere else. So this is a nonsensical, because essentially the other countries' taxes are rendered optional. Why pay the whole thing, when you can do some corporate gymnastics and pay less to a tax haven?
It comes down to what in the socialist context is referred to as solidarity. In this case, if you want to tax something, everyone has to agree to that. If there are notable exceptions, it doesn't work. Malta is an example of a notable exception.