> Schemes like Horizon Europe make scientific research easier in similar ways.
Roads allow any vehicle anyone built to work on them. Having EU-specific roads that cars built in the EU can easily drive on, while other cars require significant modification, would be a better analogy.
This analogy doesn't work, because it assumes that "roads any vehicle can drive on" is the default position outside the EU. But that's precisely not the case here - the default position in the Non-EU world is that cross-border cooperation and financing bears prohibitive problems. So Horizon is a significant improvement on the default position.
If you want roads as metaphor. Here it is: Roads profit those who are based along the road. A road between cities A and B profits those living and doing business in A and B more than anybody else living in a third city which is not connected to the road. That is just a matter of fact not a deliberate design decision to exclude someone.
The Horizon research framework exists to make it easier to form research projects across a set of countries. Everybody from a thirdparty country is at a disadvantage. But that is not because they, somebody in Brussels, wants to exclude someone. It is because the thirdparty country didn't put in the work to align it's local rules to the rules of the treaty.
Roads only help people who are in that location. The EU-specific roads (or programs) only help people driving (or researching) in the EU (and affiliated countries).
Roads allow any vehicle anyone built to work on them. Having EU-specific roads that cars built in the EU can easily drive on, while other cars require significant modification, would be a better analogy.