That doesn't mean 20% is their profit. It means all the rest of their overhead has fit into that 20%, such as hosting infrastructure, office space, labor, marketing, etc.

Oh no, how will they cover overhead with 20% of tens of billions of dollars!?

Costco is famously about 2% or so, which is basically the entirety of their membership fee revenue, iirc.

80% of a very large number is an even larger number.