In practice, these countries implement already a lot of EU law. It isn't that difficult for say a Switzerland to join the EU and they have good reasons to, as access to programs like Horizon is a huge benefit. The economies of these countries are quite interwoven with the second largest economy of the world. The EU market comes with rules but is is a very big win for neighboring countries. In fact, Switzerland backtracking on previous accession tracks and thus not qualifying anymore for Horizon etc is causing some serious regrets, so I won't be surprised if Switzerland bites the bullet somewhere in the future.

Secondly, the world got a lot more unstable since the US is pushing for a lawless might-makes-right world and taking an increasingly predatory posture there. From that perspective, the EU is becoming even more relevant. Poignant example is Canada taking more and more steps to integrate their economy with the EU, as well as to become part of its security architecture.

UPDATE: Leaving the Horizon program has apparently been too painful [1], seems the Swiss were retroactively allowed back from 2025 [2]. I don't know about Horizon 2028 though.

1. https://sifted.eu/articles/switzerland-startup-talent-brain-...

2. https://research-and-innovation.ec.europa.eu/strategy/strate...