I think there is a distinction there, Leopard. Shoes, clothing, etc. can fall under the broad category of equipment. Athletes are allowed to use equipment to enhance their performance within certain limits set by each sport.
Mariah Scary said that she was against substances that enhanced performance. A fair understanding of substance as it is used today is something that is injested and more commonaly a drug that is injested.
I don't think that drugs are banned only because they are dangerous, but also because it seems basically unfair and unnatural. For example, I think comtemporary baseball has been degraded by the use of drugs. Baseball is an historic kind of sport where records and statistics are take very seriously. Artificial enhancement of performance of current players is actually debasing the achievements of past players.
I think that athletics does not name every single substance because substances can be altered slightly and called different names. Certain categories of substances are prohibited and examples of those drugs are given. Stimulants have long been banned.
THG was not specifically banned either, but anyone who was taking it knew they were doing wrong.