Because at one point you did. And the existence of those places worked on removing barriers of trade. And now those places are being dismantled while the barriers of trade are already removed.
So you get the luxury to look at it through the lens of the present, ignoring how it came to be completely.
At this point financial centers offer different collections of favorable regulations that you can choose at your own whim.
Separate jurisdictions shift nuances of law around and compete on this still.
For example, many people access the US markets through Delaware "because they heard" and have no idea what the other 49 states, 1 district, and 5 territories offer despite having complete autonomy to compete over the last 30 years.
Some of those 55 jurisdictions are faster, cheaper, have Chancery courts, have favorable court rulings completely opposite of Delaware, can lean on Delaware case law if desired, have newer and more interesting business types you can create, may be more private and anonymous, may be better for your business.
Thats how centers develop and their utility. Its mostly the ease of getting the local government to listen to the desires of ephemeral entrepreneurs.