Cheap cheap labor
Why do american firms produce shoes in Vietnam (nike, new balance, etc.)?
Extremely cheap labor including force labor on children, no to lax government regulations, no unions that demand high fees and encourage very little work, while demanding very high wages, while looting the members accounts. Some Americans are refusing to work 40 hours a week. While Chinese are sometimes willing and force to work 80-90 hours a week for pennies.
Nike its all about the 💵.
No kid in America dreams to work on an assembly line doing monotonous manual tasks 12 hours a day for minimum wage. No American parent in their right mind would dream of their kids working an assembly line. Other than BOEING or other highly skilled manufacturing like that of Germany.
An American kid might dream of designing shoes for Nike (Senior Footwear Designer ( $128k a year). As a young adult they might look at being a business analyst for New Balance out of college ($80k a year).
There's nothing in effect to directly stop YOU or anybody to start a company producing cheap sneakers in the USA. Will it be successful? Doubt it.