The value being written was composed from multiple inputs. Instead of instructions to combine those inputs into a register and store them, it performed multiple

The value being written was composed from multiple inputs. Instead of instructions to combine those inputs into a register and store them, it performed multiple partial stores of the values it was composed from. Think two u16s being ORed into a u32. Maybe it chose this optimization due to register pressure, and not wanting to spill values that were still going to be used?