Technical debt can exist in any product and for a variety of reasons: inexperience, frequent employee churn, lack of leadership, frequent change of product direction, etc. Your comment implies that the technical debt is with Clojure the language or because of it. Beware of single-cause explanations of inherently complex problems.
I've designed and worked on systems with both OOP and functional-style code. Clojure is a tool that very much helps minimize technical debt. I think the minimal use of managed state in Clojure plays a crucial part.
Having done a good amount of looking through the Clojure language code itself, there's very little (if any) technical debt there.