Why do the Z-fighters never use King Kai's techniques?

[Legendary Saiya-Jin]

and that's even if you give the humans sane power levels rather than this arbitrary "nobody ever passed Ginyu/1st-form Freeza" nonsense that some people here seem to go by.)

There is nothing sane or sensible about giving them powers above Ginyu/ Frieza.

[DragonBallFan8001]

I don't think that Tenshinhan and Yamcha were too weak to learn the Kaioken. Yamcha got to King Kai's planet with a power level of 1,440, if I'm not mistaken, and he stayed there almost just as long as Goku did, so he most likely left with a power level that's higher than 8,000, most likely allowing him (depending on his ability to control his own energy), to use a Kaioken times 4.

Tenshinhan stayed almost twice as long, so he would probably have left with a power level of approximately 72,000, if he got stronger at the same rate as Goku did, while training on King Kai's planet. Considering Tenshinhan is very good at controlling his own energy (he can use techniques like the Kikoho and the Mafuba, after all), I think Tenshinhan would definitely be able to use a Kaioken times 10.
In case he was really able to use the Kaioken without putting any strain on his body, somehow, his power level could be 720,000. Maybe Tenshinhan didn't learn the Genki Dama, because he wanted to perfect his ability to use the power of Kaioken continuously.

Even so, they were very weak compared to the current villains, so much so that even if they had perfected the techniques, they would be useless anyway. Would a Kaio Ken x20 Tenshinhan done any good against Androids #19/20? No, of course it wouldn't. And like I said previously, the Genki would be worthless as none of the Z Fighters that went to North Kai's planet would have been able to last long enough to throw the thing.

Considering Tenshinhan would probably have gotten about 10 times as strong in the three years between the fight against Mecha Freeza and the Androids, and considering he probably was able to use a Kaioken times 20, after increasing his power that much, his power level could very well be 14,400,000, when using the Kaioken times 20.

If that's Tenshinhan's power level, I think he'd be stronger than Goku, Trunks and Vegeta's base forms, and also stronger than Piccolo and Gohan, and stronger than Android 19 and 20. After all, he never really seemed scared of the Androids, and Android 20's guess that Tenshinhan was weaker than Piccolo could've been due to Tenshinhan not using his Kaioken power outside of battle.

[KameRule]

If anything, they'd be better suited for a Genki Dama than Goku would. Goku could be there at the frontlines, drawing fire away from whoever is preparing the Genki Dama, so that whoever the target is won't even notice until it's too late. When it came to Goku, there usually wasn't anyone around of equal footing to the enemy to be able to hold them off long enough for him to charge it. When using it against Freeza, he had Piccolo, Gohan, and Kuririn for all of one attack a piece, and against Buu, he had Ssj2 Vegeta and Mr. Buu, neither able to put up any lasting fight against him (Mr. Buu survived as long as he did just because he was a Buu). However, if it were Goku actually buying time, then things would likely be better.

Well, their enemies could probably sense a huge freaking Genki Dama over their heads. Remember Frieza couldn't sense energy.

[Zillamon51]

Not only does it make no sense that King Kai didn't train the other Z-Fighters in advanced techniques, it makes no sense that Goku himself never passed on any of his special moves. While training to face the Androids, or in the Time Chamber, he certainly should have taught at least Gohan to use Instant Transmission. How useful a technique is that? Very!

[CordonBloo]

Goku has always had like weird psychic abilities that aren't touched on that much in the series. He 'learned' telepathy, like who does that? Goku is really gifted and special, I mean what I'm saying is maybe he considered teaching Gohan Teleportation but Gohan just didn't get it. I like to think that he passed on a lot of his unique techniques to Oob, the Kaio-Ken would really suit Oob I think.

But yeah, Goku is special!

[Darkprince410]

If anything, they'd be better suited for a Genki Dama than Goku would. Goku could be there at the frontlines, drawing fire away from whoever is preparing the Genki Dama, so that whoever the target is won't even notice until it's too late. When it came to Goku, there usually wasn't anyone around of equal footing to the enemy to be able to hold them off long enough for him to charge it. When using it against Freeza, he had Piccolo, Gohan, and Kuririn for all of one attack a piece, and against Buu, he had Ssj2 Vegeta and Mr. Buu, neither able to put up any lasting fight against him (Mr. Buu survived as long as he did just because he was a Buu). However, if it were Goku actually buying time, then things would likely be better.

Well, their enemies could probably sense a huge freaking Genki Dama over their heads. Remember Freeza couldn't sense energy.

That's actually more my point. If you had to have someone gathering ki for a Genki Dama and someone else trying to fight the enemy to give you time to finish completing it, wouldn't you want some of your strongest guys out in front fighting while you let your weaker ones be in the back?

[TrunksTrevelyan0064]

That's actually more my point. If you had to have someone gathering ki for a Genki Dama and someone else trying to fight the enemy to give you time to finish completing it, wouldn't you want some of your strongest guys out in front fighting while you let your weaker ones be in the back?

They often tend to go by a sort of "warrior's code" to leave it up to one person to fight the enemy. Though there are exceptions, like with Raditz. But what I'm trying to say is, if Goku is fighting someone one on one, he wouldn't like for his buddy to gather Genki Dama energy in the back, unless maybe that was the absolute only way to win. Sure, Gohan or Trunks might use that strategy, but Goku or Vegeta would much rather win the fight on their own.