That a “return ticket” is just two singles bought together, and thus priced as two singles, is pretty much the norm with every railway in Europe, except for the UK.
So this is not something unusual. Some railways do allow you to buy an outward and a return for two different dates in one transaction, but in those cases you are still basically just buying two tickets. This is offered for convenience, and does not result in a discount.
On SBB you have to buy both tickets separately. It is a minor inconvenience. Most people wait with buying tickets till a few minutes before travel here, so it is a feature that is not realy missed.