It probably lets them scrap large amounts of FM transmitters, relays, broadcasting hardware and maintenance. I assume in a mountainous country such as Switzerland this adds up to quite a lot
But DAB is already deployed, removing the FM part will probably allow them to spare money. I think the transmitters are managed by someone else than SRF (maybe Swisscom broadcast), as any service it can be pretty expensive. This said, I'm not happy about the removal of FM. Now I want to find out what's the cheapest way to broadcast the whole FM band at once using an SDR (inside my house).