Plates are flat objects sitting on THICK thermal masses called kiln shelves. When the kiln is heated up, the exposed thin plate rims will heat pretty quickly and evenly. But because of the thermal mass of the plate bottom and the kiln shelf, the poor circulation with kiln atmosphere on the back side of the plate, and the fact that radiant heat transfer (particularly if this is an electric kiln) is not typically hitting even the plates top surface well......... it can cause the plates (and low wide bowls) to crack. Rim expands... bottom does not at the same time.
Almost the same effect happens in reverse if ther kiln is cooled too quickly due to the cooling retarding of the thermal mass of the plate bottom on the kiln shelf. Rim contractss... bottom does not at the same time.