It's not a dumb question. I think it's just a matter of commonly used conversions.
Off the top of my head I know that there are 2.54cm to an inch. I couldn't tell you offhand what 36 times that is.
Similarly pretty much everyone knows there are 12 inches to a foot and 3 feet to a yard. (I'd like to think that anyway)
Fewer folks would immediately know there are 36 inches to a yard.
If you have a conversion factor from cm directly to yards at your fingertips go ahead and use it but it's usually easiest to just remember the base conversions and daisy chain them like this.