Why haven‘t all those doomsayers closed down their businesses long before the GDPR?

There are varying degrees to which people see laws as affecting them. Small business tech owners, when a law says they have work to do, are going to feel affected. If there was a securities or accounting law that felt similarly overreaching one could expect a similar reaction. This is especially true if there is an alternative (locking out markets) that is easier. It's not helpful to try and compare the situations. It's also not fair to consider people weighing the costs of these laws as doomsayers. They aren't closing down their business, they're just restricting it to more business-friendly environments in their view.

People in other parts of the world have gotten used to that. As a current example, see US threats re: European business with Iran.

Even if the GDPR were overreaching (and I vigorously dispute that notion), it would simply be a taste of America‘s own medicine.