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Labneh is also called yoghurt cheese. It is traditionally made by draining yoghurt. The store bought labneh however has many additional ingredients in addition to milk and live cultures which make up yoghurt, such as cream, skim milk and whey protein concentrate.
Why do manufactures use cream, skim milk and whey protein concentrate instead of simply whole milk which does not require additional processing?
Commercial food production has a stronger focus on consistency than homemade stuff; a company making a food product usually wants to be very sure that they can offer exactly the same product every time, regardless of time of year, which facility it was made at, and other factors.
As such, many companies will try to ensure consistency by strictly controlling their input ingredients; instead of culturing regular whole milk which could vary based on supplier or time of year, they will mix together various parts of milk (the cream, skim milk, and whey protein you mentioned) to get a mixture with very precise levels of protein, fat, sugars and such, so that they know it will always turn into the same yogurt, and therefore into the same labneh once drained.
