Tax rate on a particular GDP is supposed to match to a debt burden the way your income is matched to the size of a mortgage the bank is going to give you

They need it to optimize the debt burden they can levy on a country without forcing default

Obviously they also secure the loan in other ways (just like a mortgage) and they have violent enforcers (just like a sheriff) to repossess collateral in a default

Sometimes they’ll even bomb your country in a “burnt offering” and then pretend they didn’t call it that, and actually the “burnt offering” is what you did to them