The yeast is very adaptable and difficult to kill.
Also, there can be underlying causes which need to be taken care of before yeast can be brought under control. I think there are a fair number of people out there who focus only on the yeast while ignoring the possibility that the yeast may be a symptom of another problem (like heavy metal toxicity).
I think that this problem is extremely variable and not everyone needs to follow the same path to take care of it, but for many people it would take a strict anti-yeast diet to really bring the yeast symptoms under control. Unfortunately there are quite a few people who need to but can't or won't follow the diet strictly. Some people seem to have genuine health problems caused or worsened by following the diet while others make excuses for why the won't.
What sometimes annoys me is that I've read some people who didn't follow the anti-yeast protocol properly and then complained that the protocol didn't work so yeast must not be their problem. Perhaps they should try an actual anti-yeast program before they decide if it works or not.
Something else that I think a fair number of people fail to do is recognize that eating the same vegetable too often can make a person intolerant to it. They continue to eat that vegetable because it's "safe" on the diet and never feel better because they are still feeding the yeast. I had this trouble in the beginning of all this until I began to strictly rotate vegetables I ate.
It took me 5 days of a strict anti-yeast diet while taking a yeast killer before I saw the dead yeast in my stool and felt much, much better. It didn't cure me since I couldn't break the diet without feeling worse. It wasn't until I chelated for a while that I could break the diet with few side effects. I can eat things like pizza now, but I still experience some effects if I break the diet too much. I'm very hopeful that I'll be able to finish all of this soon.