What's the noun for interestless? Here's the word you're looking for.
interest
(uncountable, finance) The price paid for obtaining, or price received for providing, money or goods in a credittransaction, calculated as a fraction of the amount or value of what was borrowed. [from earlier 16th c.]
(uncountable) A great attention and concern from someone or something; intellectual curiosity. [from later 18th c.]
(uncountable) Attention that is given to or received from someone or something.
“She could not be sure, but she thought the expression on his face had changed from a natural friendliness to coldness, lack of interestedness, as if he had just remembered that he should not be amiable.”
“Perhaps we all have a varying aptitude for interestedness and these researchers – as a hand-picked super-interested elite – can coax it out.”
“The concept of director interestedness comes into play during a potential conflict of interest situation.”