I'm not affiliated with IB so don't take what I say as defending them. This goes for a number of companies. I have no clue as to what it costs IB to make/have made, their products. They may have a small mark up to keep the price of said soap low and more appealing financially to a new user/budget conscious customer. Regardless of weight of the product they may have a minimum shipping fee to help cover the costs of both shipping and the soap it's self.
How many times have you seen something on line, went through the entire checkout process, and found the shipping the be a couple dollars extra than what you figured? By that time most people just say heck with it and accept that couple extra and be done. Just simple economics and human nature.
"He who hasn't faced adversity doesn't know his true strength. "