String, this is just not true.
I can see Red Sea Shadows point that there might be stretches of Red Sea coast that are not dived, for different reasons, and that you won't find a stunning reef wall everywhere you jump into the water, but I have dived in so many places that aren't named dive sites, and there was always something to see. I can see that there might be places with next to nothing, due to currents, topography, etc., so nevermind.
SO, let's name some Nuweiba dive sites (I try to put them in North to South order):
Castle Beach, Ras Shaitan, Angelfish, The Valley, Outside Rock Sea, Rock Sea, Nuweiba Canyon, Ma'agana, Um Um Raicher, Labyrinth, T-Reef, Ray Hole, Swisscare Reef, Sha'ab Elaria, MFO North, Pipeline, "House Reef", Sinkers, Abu Lou Lou, Ray's Place, Farrah Shore, Myserique, EL Hibeq, Ras Mumlah, Ras Abu Galum.
These are 25 dive sites, and I dived them all. They are all different and some have been named "within the top-ten of the Red Sea" by an American dive magazine lately. A marine biologist I met, from the University of Hawaii, told me that the reef quality she saw is amazing. I guess this is an expert opinion to trust. Nuweiba has huge coral gardens and some steep wall dives, plus the two canyons (one shallow one tech only). Of course some of the reefs are "small", but that does not mean that they are worse than others, nor does it mean that they are all that small.
There are dive sites everywhere in the Red Sea, where you dive around relatively small pinnacles. Sometimes those are even the dives where you see the most, because you concentrate on a much smaller area. From what I have seen of Nuweiba, some coral gardens are really huge, and some easily good for multiple dives.
Here is what I have seen and photographed in Nuweiba:
fuzzy ghost pipefish, ornate ghost pipefish, different sea horses, red, green, white, black and purple frog fish (from 2cm to 45cm), red sea walkman, stargazer, toad fish, ... plus all the usual Red Sea stuff like turtles, rays, snappers, barracudas, napoleon wrasses, batfish, jackfish, goat fish, different puffer fish etc. etc.
For me this is quite plenty, plus all the amazing rare stuff.
I find 5 dive centres in Nuweiba, and given that it is not a mass-tourism destination, this is good. One is PADI 5* IDC centre and TDI facility. What else do you want? I very much prefer a small place that is friendly, individual and has small groups, because this means the most customer service.
I guess, in the end it comes down to personal preference, but I can see as well that people from Dahab would much rather have people go there than to Nuweiba, and therefore cannot admit that Nuweiba is a nice place to spend a quality dive vacation, too.