Commercial pilots spend much more time in the air, that would offset any additional protection. Which is minimal anyway. A thin layer of aluminium compared to plexiglass or glass. For Alpha particles either would give perfect protection, beta would be about the same. Neither hardly make it through our magnetic field anyway.
For gamma rays I wonder if Aluminium wouldn't trigger more bremsstrahlung, I remember reading somewhere that that is more prevalent in metal, but I'm not sure now.
I'm not sure what their cancer rates are though.
The reason for the higher time in the air is that fighters really need a ton of maintenance. Every flight hour means 10-15 hours of maintenance. For commercial jets it's like the opposite.