As I understand it, concept cars are built in very small numbers - as in, a handful maybe - they are hand built and so even a major manufacturer can’t justify the expense of building very many. As a result, they’re mainly utilized internally or shown at the major international auto shows only, at least until they’ve outlived their usefulness- at which point, most are sadly sent to the crusher.
More than this, historically, concepts by US automakers are intended for a multitude of things.
Show cars are frequently made for public display to gauge the public's reaction to
styling, feature, technological, and other aspects.
If functional, they're often made as testbeds for technology, performance, new implementations
of drivetrain, and much more. Strong public reaction to styling often causes the manufacturers
to use all or portions of styling in future production vehicles.
This is evident in the Chronos I posted, with the influence easily seen in the current 300.
Within recent decades, the creators of these have realized that there are some good reasons
to preserve them, and they often are donated to museums or similar institutions, while some
manufacturers have created their own collections for the purpose of public display.
Functional concepts frequently are displayed in shows in many places,
the Chronos again being one such example.