If high alloy tool/stainless steels (modern super steels) out perform more simple steels when it comes to fine edge holding. Why aren't more high end straight razors or straight razor enthusiasts and makers using them on their blades?
Because they seriously underperform simple steels when it comes to actually taking a fine edge.
In fact, most super steels contain large carbides that make it not only much more difficult (I'd say nearly impossible for something like a razor) to sharpen, they also, by their size and presence, make it impossible to achieve a truly fine edge.
Some super steels are much better in this regard than in others, but from my wood working experience, I'd say this:
1. Super steels take a good edge and hold it a long time. Simple steels take an exceptionally good edge, which degrades only slightly faster than super steels in my experience, which is mostly with push cuts through wood and leather working, or kitchen knives.
2. Very high quality simple steels, such as Japanese White Paper steel, are just all around superior in both edge retention and their ability to being able to take an absurdly keen edge. Even though these steels are harder than many super steels, I can still sharpen them just fine on natural stones.
3. I have noticed, again in woodworking, that steels with large carbides like A2 tend to form micro chips where those carbides break off at the cutting edge. This is probably largely responsible for their diminishing performance whereby which they get sharp, and then dull to a certain degree and hold on to a "kinda sorta sharp" edge for a longer time.
But, take everything with a grain of salt. I'm not the most knowledgeable person here with regards to steels, and I'm pretty new to razors. I just have a heck of a lot of experience pushing blades of various metals through wood and leather until they're very dull and then making them sharp again by many different methods. I've commented on woodworking forums about my observations, and the issue with carbides is the explanation I was given by someone very knowledgeable of different steels and metal working.