Starting this year, cycling on Swiss trains is no longer as spontaneous as it used to be. In a good part of the network, including Graubünden, central Switzerland, Bernese Oberland, Valais and several services in Romandy, the reservation of a place is mandatory. It's not a suggestion. If you board the train without having confirmed it, you risk being forced to get off at the next stop. The system has been implemented in some sections for some time and has been extended precisely because demand has overflowed the capacity of the authorized wagons.
The reservation is made in the CFF app when buying the ticket, or at the station counters. The price is symbolic. What is not symbolic is to arrive at the platform convinced that it is enough to have the general pass and discover that your bike has no right to climb. This is not theory: it happens every weekend in the mountain resorts between May and October, when the influx of cyclists multiplies the pressure on the authorized wagons.
The logic is the same as always: Switzerland regulates. It does not prohibit the use of bicycles on the train, far from it. What it does is manage the flow with clear rules that, if you know them, do not pose any problem. The problem is that many people have been climbing without reserve for years because no one had stopped them until the rule changed. The system does not forgive cluelessness, but it is also not difficult to use once you know it exists.