My understanding is that in the 90s and 2000s publishers started realizing that they could sell bare bones textbooks and then sell those problem examples in compendiums, effectively double dipping on each student.
> In addition to well-explained solutions, this manual includes corrections and clarifications to the classic textbook Linear Algebra, second edition, by Kenneth Hoffman and Ray Kunze.
I think this is actually fair; even Strang, after all, provides answers to only select problem sets (e.g. only odd problem sets in Linear Algebra if I recall correctly) though to be fair to Strang, it seems to me that in his case, it's more a matter of "if you are unsure, come and ask me" and probably not the case of maximizing profits.
Edit: For example, books like this: https://www.amazon.com/-/es/Gregory-Grant/dp/B08FP7SNZJ
> In addition to well-explained solutions, this manual includes corrections and clarifications to the classic textbook Linear Algebra, second edition, by Kenneth Hoffman and Ray Kunze.