As parent said, in international terms, you can effectively shift profits wherever you want, assuming a sufficiently large and non-physical business. Which led to this entire recent mess.
It was less of a problem when steel needed to be bought here, and goods needed to be sold here. Can't very well claim that here is actually there.
But with intangible goods, you can! Who's to say what the fair price of using Google Nigeria using Google's brand is?
Which led to a game of "Where to put the profits, without being too obvious about it?" Which led to a race to the bottom in tax rates to attract business.
Effectively, this base rate is good for major developed countries (who typically didn't need to have the lowest rates), international businesses (who had to play convoluted shell games, without ever knowing the true rules, to stay competitive), and even smaller or developing countries (who now don't have to cut their own throats to attract businesses).
Which is probably why an agreement happened. Nobody liked the old game, but it was a competitive necessity.