My own airline had an incident recently where one of our senior captains became so disoriented taking off at night over water that he thought every flight instrument onboard had become unreliable (VERY unlikely). He dove toward the ground but fortunately managed to land before a disaster occurred. His First Officer stated that she knew the problem wasn’t the flight instruments, but didn’t correct the captain adequately.
You’re right, these experienced pilots should know better, but incidents do happen.
In addition to what huslage said, there’s something called an aerodynamic stall: in very oversimplified terms, if you go up too steeply without adequate thrust your wings will produce dramatically less lift all at once.
Or even worse, and more likely, just one one side (wing drop). Then you're really doomed. Happened recently on an ATR I think.
I did some flying with a hood - no ability to see outside but I could see instruments. It was uncanny, and I got totally disoriented.
The only thing that saved me is that as a former sim jockey I was used to flying just on the instruments and I knew it was very unlikely that they went wrong just as I was flying blind. So I focussed on the instruments and ignored the feeling that the plane was literally flying on its side.
You’re right, these experienced pilots should know better, but incidents do happen.