If the effectiveness of redistributionary tax policies are capital flight, then why not just seize the assets of people fleeing abroad?

This seems very effective and easy to implement. Seize their shares, assets and accounts.

Assume the US implements this and does so immediately and without forewarning which may allow capital flight in the period before implementation. Established high income individuals would not leave, as they would lose all their assets. People who have the talent/potential to become high income will not leave as they are not yet high income.

In net, individuals who choose to flee anyways run the risk of losing everything to save a comparatively tiny portion of their net worth from being taxed away. Not to mention the US is uniquely bequeathed with established (more than self sustaining) capital markets to allow entrepreneurship.