If they had a 128GB option you could say the same thing about the lack of a 96GB option. There are hundreds of billions of potential storage sizes in this range. Apple has to be practical and choose some very small selection of storage options.
How many professional photographers and videographers do you think are using an iPhone to perform their work? Pro is not a gated marketing term with a legally defined meaning like Champagne.
But who's classifying it as PRO? Professionals definitely aren't, and that's what matters. They aren't walking around with any phone as their main tool. Let Apple call their phones rocket ships if the name fits; astronauts won't care.
i'm inclined to believe that pro is aimed at people willing to drop a ton of money that think they're pro more than they actually do professional work, and that's sort of been a lot of apple's theme around their "pro" products regarding photography
It is just an upgrade to an existing lineup of Xs+Max, but with a reworked naming scheme (similar to iPad vs. iPad Pro). It is about as Pro as Xs+Max were.
Do you see a lot of artists using iPad Pro as their main tool? Me neither, but I do see a lot of them using it as their secondary tool that also doubles as a general-purpose personal computing device. Which is what, I feel, iPhone Pro lineup was made for.