Mobile CPUs embraced this hardcore; but the problem is that most of those cores don't have the programmer interfaces exposed. The most dissimilarity you get on mobile is big.LITTLE; you might occasionally get scheduled on a weaker core with better power consumption. But this is designed to be software-transparent. In contrast, the device vendor can stuff their chips full of really tiny cores designed to run exactly one program all the time.
For example, Find My's offline finding functionality runs off a coprocessor so tiny it can basically stay on forever. But nobody outside Apple gets to touch those cores. You can't ship an app that uses those cores to run a different (cross-platform) item-finding network; even on Android they're doing all the background stuff on the application processor.
Which links to the Wiki:
> These systems gain performance or energy efficiency not just by adding the same type of processors, but by adding dissimilar coprocessors
Modern CPUs have many similar cores, not dissimilar cores.