Here is my personal take on thrush and why it is so difficult
1) it is over diagnosed. A study shows that a large percentage of what is suspected of being thrush is actually a bacterial infection of the nipple area. Also for years nipple pain due to a poor latch and/or vasospasm was/is routinely diagnosed as thrush. Even IBCLC's can have a really difficult time figuring out if something is thrush or not. Treating thrush when thrush is not the problem does no good.
2) when it is thrush, it is not treated properly. For one thing, what is considered 'properly' varies from source to source. But there are protocols from breastfeeding experts that should (IMO) be followed as at least a first step by mothers and their hcps. But instead, over and over mothers are prescribed medications that have been shown to be largely ineffective, or at ineffective doses. Or baby is not treated as well, etc. For pretty up to date suggested protocols on thrush, see Jack Newman's website and the lactation textbook Breastfeeding Answers Made Simple.(your LC and maybe your local LLL leader will have this book. Don't buy it, too expensive.)
3) Everyone and their cousin has an OTC or 'homemade' remedy. Anecdotal stories of this or that that helped have their place, of course, we learn a great deal about what works from individual reports. But (imo,) individual cases should not override tried and true methods until the tried and true methods have been shown to not work. It can get very confusing. Many miracle cures are not really cures and many cases where nothing worked are misleading because the issue was not thrush in the first place! (see point 1) Also treatments fall in and out of favor for no particular reason. When I first went to LLL meetings almost 10 years ago, gentian violet was a typically suggested and used, often with success, thrush treatment. It is still suggested by breastfeeding experts but its popularity among moms is way down. Or something may be promising but there is just not enough evidence yet- A new topical 'treatment' moms are trying is coconut oil, but there are no studies or ‘official’ recommendations of it for thrush that I am aware of.
4) thrush needs to not only be treated, but prevented from recurring, or it will probably come back. Clothing, bedding, breast pads, pumps, bottles, bottle nipples all must by cleaned well and often during treatment to prevent reoccurrence. Baby and mom must be treated, contact with other family members and even pets can cause a reoccurrence if they are not treated.