Why do pet stores sell so many common plecos? It seems to me that they would sell more of the smaller variety of pleco but 20" commons seem to be the most popular. Does anyone know why. I ask because I have talked to a lot of people who bot commons not knowing how big they get. My theory is that the pet stores sell them in hopes of tricking you into buying bigger tanks as the fish grows.
Maybe they are pretty easy to breed? Who knows. Many people just think they always need a "sucker fish" in their tank to keep it clean. In reality, they probably make most tanks dirtier than clean. 

). They're very common over here, more so than the common pleco I would say, probably because they breed so easily it's hard to even give them away. How's the situation for them in the UK and US?