"Bigger than Google" isn't an interesting metric. A better comparison would be to other insurance companies: Progressive Insurance has ~30k, Allstate ~43k, and State Farm ~70k.
Roughly half of Social Security's workforce consists of insurance administrators, who respond to and adjudicate claims and set individual citizens up with their benefits. Unlike State Farm, basically every American interfaces in some way with Social Security.
Again, an example of how a site full of numbers and line graphs can mislead by failing to provide context, while pretending to present a complete picture.