At that point Takanohana had gone through numerous ailments and was clearly declining. Had he opt not to go into senshuraku with two chances to win, the basho would have finished with an incredible dud and he might very well just have ended with 21. Now then that vincing, remarkably emotional posture and facial expression after the ketteisen is a lasting memory in a great career otherwise without much flair. He was clearly badly injured going into day 15, what further damage was done, who knows but he must have felt that was likely the last hooray.
As for these other people, someone like Endo would never get to same heights, kensho and popularity as he has been after a long time off, Maybe it was calculated on his part to try to ride the wave a bit longer. Who knows if he even wants to duke it out for a decade. Most rikishi carry some injuries. Terunofuji on the other hand sure seems like someone who should not have competed as of late.