Higher-molecular-weight sodium hyaluronate sits at the surface and holds water there; the hydrolyzed, lower-molecular-weight form is included specifically because it is formulated to reach further into the viable epidermis, where the two are understood to behave differently rather than as one interchangeable ingredient at two prices.
Niacinamide is included at a supporting level here too — this is a hydration serum first, and the anchor list above reflects that ordering.