[FastFT]

Couple of likely reasons:

1. Process limitations (no high voltage devices, poor analog characteristics, limited resistor choice, etc)

2. The skill set for power device/analog IC design is very different than digital design (and harder to recruit for as the talent base is relatively small).

3. On chip power converters universally suffer from poor inductor quality which trashes your efficiency (thus increasing cooling demands as well).

From a business perspective it would be quite risky and likely not cost effective.

[bgnn]

TSMC 7nm has all the required stuff to build a DC-DC converter from 3V or 1.8V. Nobody would use on-chip inductors for high power DC-DC.

As for skillset, there are a bunch of IP companies with silicon proven designs available. I'm sure they didn't design their SERDES or PLL(s) in-house either.