You would get some amount of increased performance from dual 8 GB chips, yes, but getting 1x16 GB chip allows you to upgrade to 32 GB later for the cost of 1 more 16 GB chip, instead of having to get a 2x16 GB set. Can be much more economical, especially with prices these days.
Wouldn’t two half-sized sticks perform better?
I thought dual-channel RAM was a thing at least as far back as the original Socket A nForce chipset.
You would get some amount of increased performance from dual 8 GB chips, yes, but getting 1x16 GB chip allows you to upgrade to 32 GB later for the cost of 1 more 16 GB chip, instead of having to get a 2x16 GB set. Can be much more economical, especially with prices these days.