I would explain it like this-----
There are no steroids that are made specifically for you to lose weight---
There are steroids that make you gain lean mass rather than bulk mass(which carries alot of water weight)
Therefore people who take these "cutting" drugs are usually doing cardio, dieting, and trying to loose weight(fat), therefore these are better drug choices--giving lean mass--without the problem of water weight
People who are fat are not going to be ripped simply by taking halo,
winny, etc. without alot of dieting and cardio
These "cutting" drugs also carry a shorter half life in the body, therefore forcing the user to use more of the drug
That is how I would explain it---dont know if that is what you are looking for