1.) Financial debt does not slow you down, technical debt does slow down work. Depending on how messy the system is, it can kick as soon as 3 months into development. It can make project fail or slow to develop and it is insidious - it is sometimes hard to see that things could be faster from CTO position.
2.) If you have money it is easy to pay financial debt and it happens instantly. Even if you have time, it may be hard to impossible to fix technical debt. The engineers might just create bigger mess in their attempt to clean things up, they may cause bugs, miss whole features etc. But most often, they just don't end with all that much cleaner system, because the mess is result of broken process or other systematic reasons or missing knowledge.
3.) It is easy to know when you have financial debt. It is harder to know (for CTO) when you have technical debt. Some engineers complain about pretty much everything someone else wrote. Many decisions are actually subjective calls where there are multiple valid options and the issue is not so much "it is bad", but "I dont agree with decision". They will never all agree. Some technical debt complains are attempts to make oneself look like more attentive coder, to excuse perceived length of development or part of power struggle between engineers.