Terrible maths textbooks are the norm. Reason is jettisoned in favour of rote memorisation for reasons I've yet to divine. Maybe because it requires less of the teacher? Maybe it's assumed that it's easier for the student? Who knows. In case you haven't guessed by now, I don't share those sentiments. The "take my word for it", drill and kill style is the antithesis of mathematics who's fundamental aim has always been a deeper understanding.
This page will serve as a list of resources I've found that aim to convey a true understanding of mathematics.