The human brain is a very effective and efficacious computer. The way it attains this efficacy differs from the digital computer.
General purpose voltage references, quad op-amps, and quad comparators are almost as cheap as dirt. Is it possible that a microcontroller plus software could compete economically?
The techniques that are used to great advantage to integrate much digital functionality work far less well when attempting to integrate analog technology. Exciting new research opens the door to new ways of integrating analog building blocks for optimum performance.
As technology evolves, the definition of "programmable" analog/mixed-signal ICs has evolved as well; most users find the change to be a very good thing, despite any limitations it may impose.
Design engineers design and build things as part of product development. Sometimes, it's better to buy a subsystem already fabricated -- but which subsystem and when?