So polyphenols act as stressors.
We also know that calorie restriction can induce hormesis (in some animals). And also, that exercise also induces hormesis.
And according to the hormetic theory, it's low levels of damage that are optimal for lifespan.
So if you add several layers of hormesis, then couldn't that end up as a net bodily harm? You're adding enough stressors such that you're past the hormetic amount of additional stress.