From the description of Minions:
Minions are small, yellow creatures who have existed since the beginning of time, evolving from single-celled organisms into beings who exist only to serve history's most despicable masters.
Yet, by the end of Despicable Me, Gru has left his villainous, despicable ways behind and even becomes a hero for the AVL in Despicable Me 2 and 3.
However, the Minions never show anything but unwavering loyalty for Gru and never seek out another master after Gru becomes a good guy.
Why do the Minions remain loyal to Gru after is no longer despicable?
The simplest explanation might be that Gru treated them better than their other masters, nor did they ever accidently kill Gru. Is that supported by any supplementary materials or is there a better explanation?