Top of my head, new things have unbounded potential, existing ones have known potential. We assume the new will be better.

I think it's part of the reason stocks almost always dip after positive earnings reports. No matter how positive it's always less than idealised.

You might think there's a trick where you can sell maintenance as a new thing but you've just invented the unnecessary rewrite.

To answer your question more directly, once something has been achieved it's safe to assume someone else can achieve it also, so the focus turns to the new thing. Why else would we develop hydrogen or neutron bombs when we already had perfectly good fission ones (they got commoditised).

Given enough iteration with the same incentives, two engineering teams might end up with the same sort of product overall. We see this with airframes. We established the prototypical airframe for the commercial airliner in the 1950s and haven't changed it in 70 years since. This is good for the airline but bad for the aircraft manufacturer. The airline can now choose between boeing or airbus or anyone else for their product. If boeing had some novel plane design that wasn't copied the world over, then the airline company would be beholden to them alone.

Sounds like automobiles are -- have been, until now -- an even more long-lasting example. The basic recipe has been the same for over a century: Four wheels, two to five doors, steering wheel and other controls at one of the front seats, internal combustion engine.

Only now is one of those components, the engine, being changed out. And looking at that from this perspective, it's apparently not as humongous a change as many are now claiming: For one thing, it's just one of the four (or more?) parts of the basic recipe; for another, it's not all that new -- electric motors are in wide use elsewhere, and were one of the alternatives in rather wide use in cars, too, before the industry settled on the current recipe ~a hundred years ago.

Anyway, the "beholden to them alone" bit doesn't seem to apply to the automotive industry, since pretty much all manufacturers are in on the switch-to-electrics idea. Which begs the question: Would there really be so much of a customer lock-in in the aeronautic space either? Just like the idea of driving cars by electric motors is unpatentable, what could Boeing (or anyone else) come up with in the basic design of an aeroplane that isn't too general an idea to be protectable, or (most probably) hasn't been tried before?