Why is the first ionisation enthalpy of chromium less than that of zinc? (Atomic Number of and )

The electronic configuration of $\text{Cr}$ ($Z = 24$) is $[\text{Ar}] 3d^5 4s^1$. Loss of the first electron leaves a stable, half-filled $3d^5$ configuration. In contrast, $\text{Zn}$ ($Z = 30$) has the configuration $[\text{Ar}] 3d^{10} 4s^2$, where the first electron must be removed from a completely filled, stable $4s^2$ orbital, and $\text{Zn}$ also has a higher effective nuclear charge ($Z = 30$). Therefore, the first ionisation enthalpy of chromium is less than that of zinc.