They die for a variety of reasons, including disease, pollution, heat waves, etc. Not being half starved of essential nutrients means that they're more resilient.

From the article:

[Unaffiliated expert] said: "[...] bees face many stressors. Good nutrition is one way to improve their resilience to these threats, and in landscapes with dwindling natural forage for bees, a more complete diet supplement could be a game changer. This breakthrough discovery of key phytonutrients that, when included in feed supplements, allow sustained honey bee brood rearing has immense potential to improve outcomes for colony survival, and in turn the beekeeping businesses we rely on for our food production."