So they should put their hands in their own pockets and rock on their own and good luck with that.
We need them a whole lot less than they need us.
That is a very good question actually. Its not clear at all.
First counterpoint is that is a strategic position they’ve got, such that you really dont want someone else (China, say) operating from it. You and tje other wealthy characters in East Asia need them, if you are going to defy the Chinese.
Second is that the economic benefits from the US alliance are at this point marginal. They are marginal now. Foreign investment there isnt mostly from the US.
Third is risk -If the US is a declining power or will be scaling back its international profile, the US link will be perceived as more a danger than as insurance.