Or software that was built on outdated foundations, like frameworks and providers which may have been "in-vogue" at the product conception, but deflated or advanced into maintenance-only stage by the product release.
Let's not forget that the competition is not sleeping meanwhile, so Waterfall is equally capable of pushing out half-cooked products just to be ahead or to meet obligations/expectations.
Everyone on the project knows at one point that the resulting product will be outdated and useless, but neither side can call it quits. The one making the product needs to finish or they won't get paid, the one ordering said product can't cancel the project or they'll get sanctions according to the contract.
So they just go through the motions and produce something that'll never get used and is put straight into the bin.
Traditional Waterfall(tm) is when you spend a year in analysis, a year in specifications, a year in requirement, a year in design...
And then you put out a piece of software that's already outdated and doesn't do what the customer wanted or needed. But the company got paid anyway, so off to the next project.
With Scrum you go through the whole waterfall loop every 2-4 weeks and the customer and the team have a chance to amend any of the phases after every iteration.
This way there's less of a chance the product is completely outdated and unnecessary after the whole project (comprising of multiple waterfall loops) is done.