Well, this is just one part. In many countries the principle of equitable taxation applies and this is sometimes even written in the constitution.
E.g. everyone making over 10k > 20% tax rate. If there was a law e.g. everyone making over 10k and under 25 years old > 20% tax rate, over 25 years old > 40% tax rate, it would be unconstitutional.
Which means that a tax court or a constitutional court in a low tax jurisdiction could abolish such a law that states e.g. over 750 million turnover 15% tax, under 750 million 0% tax.
The multinational companies will not just sit there and do nothing, they will sue everywhere they can.
Another way to put pressure is to win court cases that state that if MNC's pay 15% corporate tax then all companies in that jurisdiction should pay 15% corporate tax.
That could have dire consequences and force many countries to pull out of the agreement. Just imagine if all shipping companies had to pay 15% tax regardless of where the ship is registered, then why register in Panama, or Bermuda, or Malta? You might as well register in the EU then.
Plus OK now we have Biden in the USA, these laws are supposed to take effect 2023, for sure it will be later as imagine how long it takes to pass laws in 130 countries, then we could have another American president in 2024 who has a different stance.
