One simple reason - separate from the less fun possibilities involving defense procurement politics - is that the F117 was a transition technology.
It proved that super low radar signatures were possible.
The design used those big low poly triangles not because it’s optimal (aerodynamically, very much not!) but because of the limits of computer simulation at the time.
There’s a whole fascinating story about how the theory behind low observable was developed by a Soviet scientist, published, ignored there, then implemented here.
But computer technology quickly advanced to where low-poly aircraft made airworthy by brute force were no longer necessary. See the B2 Spirit, also a very special simulation derived shape but streamlined.
It proved that super low radar signatures were possible.
The design used those big low poly triangles not because it’s optimal (aerodynamically, very much not!) but because of the limits of computer simulation at the time.
There’s a whole fascinating story about how the theory behind low observable was developed by a Soviet scientist, published, ignored there, then implemented here.
But computer technology quickly advanced to where low-poly aircraft made airworthy by brute force were no longer necessary. See the B2 Spirit, also a very special simulation derived shape but streamlined.