Answer
See explanation.
Work Step by Step
The $\alpha$ particle is bound more tightly to the nucleus than a nucleon, i.e., it has more binding energy. Energetically, it’s more favorable to emit an $\alpha$ than a single nucleon.
Furthermore, the $\alpha$ particle has no spin, but nucleons have spin 1/2. The nucleus can emit an $\alpha$ without changing its angular momentum, which facilitates the decay.
