There are some bad textbooks out there. They're often in-house productions made by non-native English speakers. Not that there's anything wrong with that, but if they're going to do something they need to do it right.
You know the sayings, "if it ain't broke, don't fix it?" and "don't re-invent the wheel", well, there are plenty of fantastic coursebooks out there, written by professional ESL writers who often have decades of experience. While I agree that you'll have to tailor the books to suit your students' needs, you might still be able to use them and just supplement a bit rather than writing a whole course.