There might be a path dependency there. Switzerland was never an EU member, and negotiated to join a number of EU institutions as a special case. It's not clear

There might be a path dependency there. Switzerland was never an EU member, and negotiated to join a number of EU institutions as a special case. It's not clear that the EU was even prepared to offer a similar deal to a departing member. Furthermore, the EU has become less and less enthusiastic about these kinds of arrangements, so even Switzerland is finding it harder to join individual deals.