I think the analogy may still be useful/interesting. It's just that with financial debt you have borrowed money, with technical debt you have borrowed time. Financial debt reduces the efficiency of future available money (interest payments), technical debt reduces the efficiency of future dev time.

I agree with your point that technical debt is a lot harder to identify, the way to pay some of it off may not be obvious and taking on that debt is not usually a conscious decision.

Sometimes you'll cut a corner to get a prototype done or hit an important deadline and there it seems more of a clear trade off, time now for pain later. But, as you say, the creeping (and inevitable?) technical debt of aging projects is less obvious. More like maintenance costs for assets and investment in rust proofing?