Why wasn't flying Raijin passed onto other shinobi by second or fourth hokage?

Question

Were Tobirama and Minato the last shinobi to perform Flying Raijin? Is there anyone else to know that jutsu?

And why was it not passed onto his students(Kakashi) /sensei(Jiraya)?

I know Jiraya mastered Rasengan after looking at Minato's Rasengan. Kakashi passed Chidori to Sasuke.Jiraya passed Rasengan to Naruto. So why did Tobirama or Minato not pass Flying Raijin onto their disciples?

Answer 1

You have to understand that not all people can master all jutsus. They have their limitation no matter how prodigious they are. Tobirama and Minato can pull off that Jutsu because they were the fastest shinobis and had insane reflexes. Their extensive use of this jutsu had earned Minato the nickname of "Konoha's Yellow Flash".

Minato would randomly appear behind enemy lines and, by seemingly being in many places at once, wipe out whole squadrons before they had time to react. By combining their naturally good reflexes with the instantaneousness of the Flying Thunder God, Tobirama could intercept and redirect a Truth-Seeking Ball mid-detonation and Minato could escape Kamui mid-capture. Minato's ability to dodge A's Lightning Release Chakra Mode led A to dub Minato the fastest ninja who ever lived.

_{Flying Thunder God Technique}

Of course, Minato or Tobirama would have wanted to teach the Jutsu to their students but they must have realized that not all can perform the Jutsu/their body can't handle the power/the body is not suited for that Jutsu nature. That's the reason, masters decide whom to teach which Jutsu (e.g. Kakashi taught Sasuke Chidori instead of Naruto).

Answer 2

Minato actually passed it, but as a variant.

As @FumiKage said everyone dosen't possess the requirements to do Flyng Raijin.

So he taught a special variant of it to Genma Shiranui, Raido Namiashi and Iwashi Tatami. They were chosen as personal bodyguards of Minato.

Those three are required to do it and they could teleport something or someone instantly with it to some place. This variant kind of works like FTG barrier Minato used to teleport the Bijuudama away during Nine-tails attack.

As in episode 323, they teleport Mei to battlefield with it.