OK, few are actively recruiting for people on those projects, as a proportion of the whole job market. A few juicy jobs there and a huge pile of less well paying ones means that any average is going to be low. The existence of those roles is great for those that have/get them, but this doesn't help the wider pool who need to use other tech to get the better wages – a situation that results in fewer newly training in c++ because those outside the pool see the low average.