Because madness is not a term so commonly used anymore?
I think we both know the link between madness/mental health and genius has been debated for much longer than you are offering.
There is this quote
"Scientists have for the first time found powerful evidence that genius may be linked with madness.
Speculation that the two may be related dates back millennia, and can be found in the writings of Aristotle, Plato and Socrates. Aristotle once claimed that "there is no great genius without a mixture of madness", but the scientific evidence for an association has been weak – until now. "
from this link... You don't have to be bipolar to be a genius – but it helps - Science, News - The Independent