Why don't segmental retaining walls need any piers or anchoring below grade?
The soil below the wall is only supporting the weight of the wall. The segmental block will have layers of geo fabric every 8" or so. Basically there is not lateral force on the wall. Since no lateral the foundation is simple, and the weight of the those big blocks is nearly the same of the soil that used to be there, bad soil has some 1000-1500 psf capacity.

You have an engineering firm, talk to them. They will talk to you about these forces for free, we actually get excited to!