That's a failure of imagination. A plausible example might be socioeconomic status (rich people live longer and also eat more expensive foods such as meat).

An environmental factor that reduces longevity and alters your sense of smell or taste in a way that affects your diet is semi-plausible (heavy metal poisoning such as cadmium can cause anosmia, which will affect food preferences), smaller but more widespread effects are possible.

Arguably we're already the beneficiaries/victims of mutations that make cooked food (that is more easily ingested and digested) taste better, but also make food subjected to combustion processes like smoking, searing, roasting, etc. (which can produce various carcinogenic polycyclic aromatic hydrocarbons as a side effect) smell and taste good.

A fanciful hypothesis would therefore be a mutation that directly increases longevity and also happens to make meat taste better (or vegetables taste worse, like they do to supertasters) and so affect dietary preferences.