He found a gravy train and stopped working hard.
gravy train
idiomAn occupation or situation that generates considerable income or benefits while requiring little effort and carrying little risk.
Origin
disputed originSaid to be originally US railroad slang, referring to an easy, short haul that paid well. The word gravy by itself was used prior to any attestable use of gravy train to characterize cushy situations. Note also phrases with hog train as a possible source of analogy.
The consultant realized his easy contract was a gravy train, so he kept it for as long as possible.
Many critics argued that the executive's position was nothing more than a lucrative gravy train, offering immense rewards for minimal oversight or genuine contribution to the firm.