There’s a lot of problems bees (both honey bee and native bees) are facing. There’s varroa mite, a virus spread by mites, pesticides, pollution, habitat loss, monoculture… a lot of stuff. However, healthy bees are more resilient, so healthy hive is much more likely to shrug off a event that could be “the straw that broke the camels back” for a weakened malnourished hive.

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.”

I expect there are dozens of different things that influence how well a hive does, some good, some bad. Maybe having better nutrition overpowers the effect of pesticides, varroa mites, etc.