Sure. But now you're talking about half a page to a full page of solution commentary for each exercise. Math textbooks at the upper-undergrad and grad level usu

Sure. But now you're talking about half a page to a full page of solution commentary for each exercise. Math textbooks at the upper-undergrad and grad level usually have 10-20 exercises per chapter. Those exercises will usually require a student to fill out a quarter to a half page for any correct solution. Even if an author was decidedly economical in how they did it, writing comprehensive solutions for each exercise would constitute another book's worth of material. Can it be done? Yes, absolutely. It is likely to be done? Almost certainly not. This is why we have solutions books - you can usually write a full book consisting only of solutions to another book's exercises.