The decay behavior of nanoscale multilayer holes on ${\text{SrTiO}}_{3}(001)$ has been studied using scanning tunneling microscopy. The multilayer hole shrinks rigidly keeping steps in bunches, which is followed by rapid decay of a bottom single or a few layers in the hole at a critical volume. Both the critical volume and the number of layers exhibiting the rapid decay increase with depth of the hole. We have found that the anomalous morphological evolution during decay is induced as a result of the competition between the curvature effect and the short-range attractive step interaction. The attractive interaction gives rise to metastable step configurations of the bunching in the hole. Then the metastable state vanishes at the critical volume due to the enhanced curvature effect with decrease in size, which causes the debunching of the steps. The presented experimental results combined with a numerical simulation based on a step-flow model allowing for attractive step interactions have revealed that the depth of the step interaction potential well on ${\text{SrTiO}}_{3}(001)$ is approximately $4.6\ifmmode\pm\else\textpm\fi{}2.0\text{ }\text{meV}$.