GaN is not appropriate for most use cases. It matters when high frequency matters, which is usually when magnetics size matters. I have also seen it used very well for ultra-low input voltages (basically energy harvesting).
It is also uncompromising and brutally difficult to get working well. GaN-FETs love to commit suicide in new and entertaining ways. And LTC7890 is not something I would want to implement in any design (though of course I'd suck it up and do it if it was the right choice).
99% of the market is traditional boring stuff because 99% of the market is well served by traditional boring stuff.
It is also uncompromising and brutally difficult to get working well. GaN-FETs love to commit suicide in new and entertaining ways. And LTC7890 is not something I would want to implement in any design (though of course I'd suck it up and do it if it was the right choice).
99% of the market is traditional boring stuff because 99% of the market is well served by traditional boring stuff.