Can't remember who made those slotted main springs but they were a major brand. Light leaf springs wear out... regularly. Before we started using coil springs in all our guns it was pretty common to have the light ones go (either weak or break) every couple of years. Sometimes only a year if unlucky yes. Sure you can get one that goes a lot longer but you always have to have a spare.
Even heavier springs that aren't lightened to the limit can just give up and break sometimes.
Coil spring kits generally will go many years before either the spring or a supporting part needs replacement and you usually get a little more warning something is up.