Stealth
As I understand it:- In the F-117 (developed decades ago) the stealth features were designed using the best mathematical tools and models of the day. Constrained effectively by the limitations of the computers of the time. This resulted in the weird angular shapes.
Today, computers are thousands of times, or maybe much more, faster. Perhaps in conjunction with better theory, this has allowed more flexibility in the choice in the profiles of the aeroplane while still being able to meet the required stealthiness.
Putting on Victor Meldrew hat - I CAN'T BELIEVE IT!!!
The pprune spell checker doesn't like "aeroplane". Or as it now turns out "pprune" either:-)
The short answer is - computers have changed everything, get with the program or go and live with the bears:-)