There are several reasons why a person (most of the times a non-doctor health professional) becomes a quack.
A quack is a person who claims to know about human body (beyond what his certificates say) and treat human illness but does not have the authority to do so. Every country has certain rules and regulations as to who can administer drugs or bring changes to human body for the betterment of human health. But the loopholes in these rules and regulations give birth to quacks.
Quacks themselves are well convinced that what they are doing is perfectly fine. They may perform quackery on their family members and even on themselves. The illusion of knowledge they possess is to be blamed; and, the loopholes in rules and regulations which justify their illusion of knowledge.
Quacks learn from doctors about alleviation of symptoms and treatment of some diseases and use their limited knowledge (of course, they themselves do not consider it limited most of the times) in a generalized manner. This is causing more harm to the society than helping it. Quackery is contributing most significantly to the bigger problems like antibiotic resistance among others.
Quackery in dentistry has a unique aspect. Dentistry is generally expensive, and quackery way too cheap. So, it is easy for dental quacks to trap people. A dentist in South Asia spends almost a quarter or even more of her time in correcting or intercepting what a quack has worsened.
It is not that what a licensed doctor does is always right. But, they understand the working of a human body in a scientific manner to way too greater extent than a quack. A quack relies on hearsay methods of treatment and drug administration. To illustrate, a dental quack may have absolutely no idea what self cure acrylic can do to soft tissues of mouth thus they use it to fill the gaps between teeth (they of course don’t know a bit about the gaps between teeth)!
Sometimes, even a licensed doctor turns into a quack! How? By doing things s/he is not supposed to do. Here, we may rephrase the definition of quacks. Quacks are those people who practice beyond their expertise.
Common people fall for quacks for two main reasons: because it’s convenient and it’s relatively cheaper. But it will be only folly to compare one’s health with money.
Aren’t doctors to be blamed for flourishing quackery (at least in Nepal and India)? Of course, they are to be blamed to some extent. Doctors are at fault in two ways. Many doctors are chasing money unethically, whether through cuts from unnecessary lab tests or through prescription of unnecessary medications for incentives by pharmaceuticals company. Some doctors are even encouraging quacks to malpractice for the monetary benefits they gain as cuts by giving their certificates to them.
Quackery is not likely to stop for many years to come in South Asia. It will survive as the dark face of service to rural communities or in the form of charlatan alternative medicine. Thus, it is entirely up to people to opt for a scientific method of treatment, administration of chemicals to their bodies and alteration of their body organs or a pseudo-scientific method of treatment.