My point is: technical debt from the point of view of Business is something that the developers themselves introduced or did not manage properly, so trying to make it look like something beyond their control ("we just found out that in the 70s someone put asbestos under the roof") will sound a bit unconvincing.
Say you run a large plumbing company, and you discover your plumbers took shortcuts on a particular job that resulted in an abundance of leaks for a given project.
The plumbing company cannot ask the plumbers for their pay back. They will have to eat the cost and fix the plumbing.
So, it's the business's problem either way. They can additionally choose to fire those plumbers if they want, which is line with your point of not believing the plumbers had no idea.
But it's still the company's debt to pay. They made the mistake of hiring people that were not capable of surfacing risks.
There are two types of tech debt in my experience, things get out of date because they weren't maintained and it's harder to do now years later than absorbing some of that work a little at a time throughout the years. And the other kind is because of poorly written code which is often caused by poor business practices and changing requirements.