Answer
There is not enough energy to create the decay products.
Work Step by Step
The $\Lambda^0$ particle has a rest energy of $1115.6~MeV$
The proton $p$ has a rest energy of $938.3~MeV$
The $K^-$ particle has a rest energy of $493.7~MeV$
The total rest energy of $p$ and $K^-$ is $1432~MeV$
The original particle is stationary, so the kinetic energy is zero.
Therefore, there is not enough energy to create the decay products.
