They put little packets of silica in supplements because it keeps the capsules and tablets dry, making it last far longer than usual. Without the silica packets, I think the expiration dates would be much shorter. In the past, they used to put cotton, does anyone remember when cotton would come out of aspirin bottles? But silica works better, so they've replaced cotton with it.
I don't think silica needs to be used in everything, but this is one instance where it's very useful.
The same packets are included in things like bags and purses and some clothing items for the same reason.