Those are exactly quickly going away. Engineers and scientists need to get paid and want job stability, while patents have a 20-year lifespan.
Nikon was on top of the world in 2008 with the D300 and the D90, but the technologies that made those possible were patented years prior. Right now, the curve is with mirrorless where Sony, Panasonic, and (now defunct) Olympus have a 10-year lead on patents. It's also with smartphones, and those technologies bubbling up. In the deep learning/ML battle, Nikon is bringing a knife to a gunfight.
On the other side, they're having massive layoffs right now. When companies have layoffs, usually they let go the bottom end of the workforce, while the top end leave voluntarily.
Nikon is continuing to patent new lens designs, but so is its competition. Nikon has excellent optics, but so does Olympus, Canon, Fuji, or Sony; they aren't exactly ahead of the pack here.
Sigma has really been pushing the edge on optics.