Quite simply: mass and class. The high concentration of at least 2x 10E9 colony-forming units ensures that sufficient cultures capable of multiplying survive the stomach passage undamaged and arrive in the intestine. In addition, they are already active due to the activation phase in water and are therefore "more robust". One possible approach could be that a pathogenic bacterium does not occur in such a high concentration, but nevertheless sometimes enough germs survive the gastric passage and make us ill.

No, it is not a problem that the powder does not dissolve completely; the insoluble microcrystalline cellulose contained in the product may leave a slight sediment in the glass.