maybe so, but perhaps it's because people are not daft enough to do it?
I had a close call earlier this year when climbing through cloud when heading north past nottingham with another aircraft doing the same thing heading east. We saw each other at the last moment as the cloud was still quite broken around the base. Made my bum clench a little!!!
It would be interesting to discover how many people will fly in solid cloud without radar cover?
I don't mind flying over it without cover but as I said before don't think it is very wise to fly in it.