I suspected that the UK had something to do with it. In the UK it is common for a day return to be only a bit more expensive than a single. However on the continent we practice “single leg pricing”, something some UK railways have now started to do as well.
Under this system a return ticket from A to B and back is just twice the price of a single ticket, and thus there is no discrimination of people for whom the return trip is the next day.
But another difference is that the system is fully integrated. You can buy a ticket from pretty much any bus stop in Switzerland to any other bus stop, and the ticket will cover the whole trip, even if there are several other buses, trains, cable cars and trams (and in one weird edge case, a helicopter) involved…
An the price schedule is such that it encourages people to get a pass, so most regular transport users do not pay for individual tickets anyway.
And we do not bother with things that increase friction, like gates, barriers, and making everyone show their pass when boarding a bus…