The algae are natural, except they are modified so you can actually absorb the B12 vitamin from them. B12 pills are less appealing within a soup than an algae.
Also, you absorb the vitamins in a natural way, instead of all at once. So it is better for your health.
Supplements are the option you choose only when you have no other, and there is research showing how it is bad for your health.
I'm guessing easier to produce than vitamin pills as well.