Myron was the creator of Jet. He was working for a mob family (Mordinos) in Reno. He talks in great detail about how he created it. I can't post the link to that speech because it is full of swearing. Just youtube it. He is very annoying. If he ever told anyone else how to make it the family would not need him anymore.
Styles I already proven using Fallout 2 as the ONLY source that jet survives Myron's death, so would you like to provide some evidence from fallout 2 that Jet doesn't survive Myron's death? The Mordino's wouldn't allow him to have that kind of leverage over there drug empire. He's a puny little wimp it wouldn't take much to beat the information out of him and they certainly would. They'd keep Myron around because he's a valuable employee so what if he shared the recipe, he'd still be the man most qualified to supervise production.
If Myron was truly necessary for Jet production then he wouldn't have been forgotten. He'd be remembered because of how hard jet is to produce. (and as I already proved using Fallout 2 as the only source, jet can survive his death).
He talks about how before Myron people were trying to grow crops to make drugs. Drug we would know. It took Myron a very long time to figure it out and get it right so it wouldn't kill people. I doubt others could figure it out. If they did they would keep it to themselves.
There was a whole team working on Jet production, the stable team even tried to develop a more powerful version called Jet Beta. So he obviously shared knowledge of how to make it. They wouldn't keep it to themselves either as they'd need help in manufacturing and distributing the drugs, plus security. If you want to expand your business you'd need to help in making it so sharing would be required. How hard jet was to develop is irrelevant. Its how hard is jet to make once you know how.
The protein extract was described as cheap, which means it easy to make(otherwise it wouldn't have been cheap). Long term production of Jet would require they know how to make the extract to keep feeding it to brahmin.
Also I still believe that the Chosen One did create a cure for jet. Jet did not seem to be a very bad problem as it was in Fallout 2 so having a cure out there could be the reason. With a cure out there Jet would not be the money maker it once was, so no reason to put the effort into making it.
Just because there's a cure for the addiction doesn't mean people wouldn't keep taking the drug because they enjoy the effects. A cure simply means you can't put a strangle hold on a population because of it. As long as people enjooy the effects of Jet they'll still be people taking it.
And as I said before, they can't actually use real world drug names in certain countires so they use Med-X and Jet instead of Methamphetamine and Morphine.