Break Week There is no plausable reason to why Luffy, Zoro, Sanji and Jinbe aren´t teaching basic haki to the rest of the crew
Opportunity cost, they specialize in what they can. If they were to start learning haki, they need to spend significant time to achieve it. Luffy the MC with highest growth (due to MC) needed 1.5 years just to get the hang of the basics and was taught by one of the best possible teachers. Don't expect the other SHPs to have that haki grasp/learning potential of Luffy/Zoro and nobody in the crew can teach like Old Man Ray. Even if you equalize the learning curve it still would require them 1.5 years to learn haki. The SHPs have spent much less time together than that from the start till now.
As for the Admiral part, even if the weaker guys learn haki, they ain't doing shit to an Admiral with their weak haki. Guys like Marco and Vista were called annoying by Akainu, what chance do Nami, Brook, Usopp have of hurting an Admiral. Haki or no haki they can't do much to an Admiral unless they have great prowess/specialization in something that can greatly effect an Admirals element. Think about Brulee trapping Kizaru when he uses his light transportation in a mirror world.
As for the Admiral part, even if the weaker guys learn haki, they ain't doing shit to an Admiral with their weak haki. Guys like Marco and Vista were called annoying by Akainu, what chance do Nami, Brook, Usopp have of hurting an Admiral. Haki or no haki they can't do much to an Admiral unless they have great prowess/specialization in something that can greatly effect an Admirals element. Think about Brulee trapping Kizaru when he uses his light transportation in a mirror world.
