just a guess, but are they getting enough water?? It seems some of my black raspberries have had similar issues but if I make a point to keep them well watered when fruit is develping then it doesn't happen.

I agree with twohuskies that you should wter them. I had tons of raspberriesin the past, except last year and this year. Last year it was very dry when the berries were developing. The leaves looked OK, so I did not water them until the berries started to dry. A lot of them did not mature. Last winter, someone cut them to less than 1 foot from the ground and very few berries are forming. In the past, I would have been picking berries for a week or 2. It is July now and they are still green.

I always heard that polination has to take place for each stone on a raspberry to get the juicy fruit you want. Might be one of my dad's old wives tales, but I guess I would Google raspberry and see what the experts say.
Pondy