Because of the shape of it. Those square wings, the boxy shape of the tail, the big jet engines hanging off the side of the fuselage... the shape was just made to return a radar echo. The only way to make that stealthy would be to wrap an F-117 around it. In other words, it's essentially impossible.
Ok. Wrap an A-117 around it.
I fail to understand how the shape of it is essential for it’s function. I understand that it’s a tough plane to down, but who is it’s shape not modifiable?