More thoughts: tech debt is low visibility, cleaning it up is discouraged, unrewarded, but also difficult and sometimes risky. Also it does take away from adding measurable value. People are not incentivized to clean it up.
Also it's never built into schedules, estimates, never prioritized or funded properly.
Explaining the need to pay some of it off is often futile, as management is simply unable to understand it if they're not engineers. It's bad for morale and productivity.