While recusing yourself you might still have a mutual interest with (some of) the other board members. E.g. imagine a Stiftung where some companies have a collective majority on the board & hand out contracts to each other. So you would have to make sure any such inappropriate collusion is also impossible.

(I’m not saying that happened in this case, but the Stiftung legal construct has been abused in such ways in the past, and when the authorities come knocking on your door you want to be able to show it didn’t.)