Paying down technical debt should be exactly as easy/hard to justify, as paying down monetary debt. They behave the same and have the same effects over time; that's why debt is such a good analogy.
I disagree, technical debt is a much more liquid quantity that can be easily paid off in as little or great a chunk as you wish. If you as a company offered to let everyone pay off tech debt with 10% of their time, but force it to be 10% on a daily basis you'll likely end up accumulating more debt - paying off monetary debt a little at a time by diverting x% of revenue to it is a particularly good way to handle debt as a private company as it ensures there's plenty to reinvest and the cost the debt is imposing is well known.
So tech debt is harder to subdivide arbitrarily, I'll buy that. And it's harder to quantify in the first place, which seems to be one of the theses of this "dear client" letter.
Not only harder to quanitify. "Tech debt" is frequently used by devs as an excuse to make changes that they'd personally like to do, but which aren't necessarily improvements, e.g. rewriting from one language to another, or rewriting code they find hard to understand because there are no comments (instead of understanding the code and adding comments).
