According to what we see in every fan made site, most players are not in their "top form", the best players usually choose the best Pokemon who suit what he wants to do, (they don't worry too much for looks, only to what the Pokemon is able to do) Garbodor can fit in many things, its very useful. However the other players give more attention to looks over everything. They want to look cool, put for example a fire Pokemon with 3 or more fire type moves, instead of balance their movesets, they are just "amateurs", they don't understand how good a Pokemon can be, how to employ a particular role, how to choose moves, how to do things, what a particular Pokemon can do. Even the people who are in the mid tier between the top players and the amateurs, already understand most things, like balancing the movesets, but they also stuck to some old, wrong ways, like believing that some Pokemon can only do one thing or that you should have only six Pokemon on an in-game, team, things like that.
But the most important reason in the case of not only Garbodor, but also, Vanilluxe, Weezing, Electrode, and others being less used is because of their looks and popularity, most people are guided by herd effect. (Muk and Alolan Muk has always being one good accepted by having a "nice look" and being owned by an important character in the anime which promotes the games. Muk is also a very good Pokemon to have but in his case is mots because of marketing matters, if Garbodor had the same promotion, it will not be a surprise if people decide to use it a lot, another good example of the marketing taking place, is the Lycanroc. Lycanroc is a bit more limited than most rock types, but is still very good, and more, he looks very beautiful and cool, and is also owned by an important character, and even before it was, he was already to well promoted, so he is one of the favorites in the last generation)
If a Pokemon is hated or loved, there are several reasons for it, but the most used is based in "what is fashionable". Most people are guided by herd effect, they hate what the most people are hating and love what the most people are loving, this happens not only in Pokemon, but in everything.