There’s not just one single answer to this, each type of plant that “can’t live in rich soil” has its own story so to speak.

One common theme is that these plants tend to be more efficient at collecting specific, necessary nutrients that are otherwise limited/lacking in their environment, and because they’d never naturally be exposed to large amounts of those nutrients, they’ve lost some or all of their ability to regulate uptake and/or to expel excesses from their tissues in comparison to other types of plants not adapted to those specific conditions.

So, when introduced to artificially high levels of these nutrients, they basically absorb the nutrient(s) until it reaches toxic/deadly levels, and then the plants lack the ability to get rid of the excess since there was never a need for such a mechanism when they evolved in their nutrient poor niche. It can lead to issues where the plants can’t maintain osmotic balance or nutrient / mineral antagonism leads to the plant being unable to absorb or make use of other vital nutrients because one of them is so out of balance.