During the last year or so we have seen commercial release of USB chargers utilizing GaN technology. For some reason it seems no products go higher than 65W. The Navitas reference platform was 65W, Delta released a 65W under the Innergie brand -- but nothing higher. Is there a technology reason for this? USB C goes up to 100W and 87W is reasonably popular because Apple shipped some of their MacBooks with such and so it's easier to market those as replacement.
If the input power of the adapter is less than 75W, you don't need a power factor correction stage (by EU and other regulations).
So they are easier to design, and they hit the largest segment of the market.
Once you need a 2 stage converter you have additional components and thermal considerations and GAN probably doesn't make as big a performance and size difference as it does with a single stage converter.
There are single stage PFC converters, but they suffer from various performance issues.
Nothing about the GaN designs prevent it from going past 65W. Navitas released a reference design before or about the same time for a GaN 150W AC-DC adapter (with a 100 to 500W target range) only it was targeted at a different market segment, high end laptops and televisions. https://www.navitassemi.com/navitas-gan-power-ics-enable-smallest-power-adapters-ultra-thin-tvs-laptops/
They even mention it in the link to provided.
The 65W reference design is a end product restraint. They chose a target power density per cc and worked backwards from there. A slightly larger or changed design would allow greater power at the cost of size and money. The 150W design uses a different topology and is more brick size instead of a cell phone cube sized charger. Less to do about engineering restrictions and more to do about marketing goals.