It may be a question of how we're describing the sound rather than a question of what we're hearing. The bridge pick up has a lot more crunch and that may be why you're describing the neck pick up as thinner. It is, but it's also more resonant and carries more treble overtones, I think. If I'm doing a bluesy solo, I almost always switch to the neck. But it is mellower as well.
(It's like trying to describe the bouquet of a good wine, isn't it?)
Well we all shine on--like the moon and the stars and the sun.
-- John Lennon