The first ingredient is water; the second ingredient is a detergent (milder than SLS). The next ingredients are Shea Butter and sunflower seed oil (good for the skin), then a humectant (attracts moisture from the air to the skin), then another surfactant/detergent - very, very mild, then a thickener/foam enhancer (people don't like to wash up with stuff that doesn't make bubbles), then Allantoin, one of my all-time favorite ingredients for skin care, then the rest are in amounts at or under 1% and are mostly to increase shelf life/prevent bacteria from growing in the product.
If that doesn't seem like an answer to you, I'll put it in plain English, but first an aside.
The Romans (well, maybe limited to the middle class and up), who had soap to wash garments with, did not use soap on their skin. Instead, they bathed in hot water, then were coated with an infused olive oil (say, lavender), then the oil was scraped from their skin with a scraper, taking away the old and (?)foul smelling, and leaving behind some of the nicer, new stuff. A couple of additional steps and they were clean. That was good skin care.
No one today washes that way. It would be prohibitively expensive and time consuming. By habit, many people would not feel clean, either, because they equate "bubbles" with "clean".
Your Cetaphil is trying to do that - replace oil removed with oil deposited - while still foaming and acting as a wash, which people expect.
Is it because, in general, it still remove your skin oil? Therefore, after all I still need to apply moisturizer. In that case, what is the different to use normal soap and then use moisturizer after that?
First, soap and detergent are different things. I'll assume you mean soap.
A very high quality soap (which you can't buy commercially) will attempt to do the same thing by superfatting the soap using oils with a great skin care profile: Jojoba oil, Macademia Nut oil, Shea butter, Cocoa butter, etc. to the point of almost not foaming (no bubbles). You would find the Cetaphil and the soap would leave you feeling about the same.
Regualar soap strips the skin of all fats and sweat, dirt, etc. Then you replace the oils stripped with new oils and the other ingredients in your moisturizer.
Does it matter? You can answer that yourself. In one scenario, you strip your skin of oils then add them back. In another, you have some good oils on your skin and you add to that. Which sounds healthier for your skin?
If you wonder why I am so opinionated on the matter, it's because I used to make skin care products for health care professionals, who often developed nasty hand dermatitis from hospital supplied skin cleansers. When my husband developed a rash that wouldn't go away - winter or summer, on vacation, using other soaps, etc., - and under a dermatologist's care for two years, biopsied twice and using steroids and other topical meds, I decided I could do better. I learned everything I could about skin health, and made some wonderful soaps and lotions that cured my husband's and others' dermatological problems. I studied skin care for about six years, and made products for five, always improving my formulas. In that very narrow area, I'd pit my knowledge against any but the best dermatologist's. In every country I've visited, their most expensive soaps are no where close to mine. They might be quadruple-milled, but they still are basically oil-stripping soaps.