Which is precisely why they haven’t.
And never mind tourism, business as well would suffer and greatly so.
France and Germanyand the UKare not going to go down that route for the sake of Croatia and Bulgaria, important as both they and the principle at hand may be.
How can there be equal reciprocity? Few US citizens choose to overstay their visas or live illegally outside the US buit millions of people from different countries settle in the US without legal status.