Aromatherapy depends on the ability to procure organic and essential oils, which are the essence of certain plants. They are not available on the mass market because deriving the oil is a considerable task, involving not only taking the oil out of the plant, but the process to turn it into actual oil is a complicated procedure, and a different processes are used depending on the plant it's being extracted from. Here is a good explanation of what an essential oil actually is, and how it's produced.
One ancient way of producing the oil is called enfleurage. It dates back to the time of the Egyptian pharaohs, and it's been done in many centuries since. It works on one simple principle: fat dissolves essential oils, and thereby absorb their aroma. But the oil is just what comes off the plant itself. A combination of that essence mixed with fat, but it's only a process to increase its potency, as it's later separated. The ancient way of doing it involved smearing a piece of glass at the bottom of a wooden crate with lard, and leaving the fresh flowers to essentially marinate the lard for a few days, meanwhile adding new flowers to the batch continually until the fat had fully absorbed the plant's oil. Then, the oil, which was called "pomade", was dissolved by alcohol. The alcohol separates the plant oil from the fat, and then it dissolves entirely, leaving just the plant essence-pure aromatic oil from the original flowers.
Whereas historically people commonly used lard from various animals, today it's common to use what is essentially vegetable fat, like palm oil. Sugar cane is used too, and these are the cleanest oils to use. So while the oil can be made from an ancient method, there are contemporary changes, or adjustments, to suit the times.
The other essential component is the flowers themselves. Enfleurage is a labour intensive means of gaining the oil, but when it's done properly with homegrown plants, the result is practically magic! It takes a great deal of plants to produce a relatively small amount of oil, so it's no surprise that more people don't do it, but when the process of enfleurage is carried out locally grown tuberoses, roses, lilies, and gardenias, the smell is something to behold, and it's got wonderful healing properties. This is the pure, organic oil, and by now it's easy to see how difficult it is to produce on scale, and therefore, how rare it is.
It shouldn't be surprising that aromatherapy has a wonderful hold on us: it's well known that memories are tightly connected to smells, and one whiff of a particular smell that has a certain association attached brings us right back to another time and place. With this in mind, once one understands what a real organic oil actually is, it's easy to see how it can make people feel recover from what's ailing them, and put them in a better headspace.