Take your favourite rock band and turn over all the musicians until no one is left from the original band. Should we expect the band to continue cranking out chart-topping hits?
There's one further factor that makes the situation even worse than the "Rock Band of Theseus." That's the fact that young software engineers are not interested in stewardship. They want to build their own projects, not fix bugs in someone else's. Across the software industry we see this lead to a continual churn, rewrites and redesigns no one wants, and a huge amount of wasted effort reinventing the wheel (and often making a worse wheel).