Here's why:

* True: The Earth's radius does indeed increase slightly due to the creation of new oceanic crust at mid-oceanic ridges. This process, called seafloor spreading, pushes existing crust away from the ridge, adding to the overall volume of the Earth.

* Caveat: The increase in radius is incredibly slow, on the order of millimeters per year. It's so small that it's practically immeasurable on a human timescale.

* Surface Area: While the overall volume of the Earth increases, the surface area remains relatively constant. This is because as new crust forms at mid-oceanic ridges, older crust is subducted back into the mantle at subduction zones. This process balances out the creation of new crust, keeping the surface area roughly the same.

In summary: While technically true that the radius and surface area are increasing due to seafloor spreading, the increase is so minimal that it's practically negligible. The surface area is effectively maintained due to the balancing effect of subduction.