This is exactly the way most lecturers would love to operate: if you don't show up to my lectures, and you fail my exam, tough.
The problem is that what actually happens is students don't show up to lectures, then they realise they don't know the material shortly before exam time and take up huge amounts of lecturers' time. We are not paid to spend five hours trying to deal with one persistent student who wants us to basically give them personal lectures on a moment's notice, and we usually have better things to do (i.e. research, which we are paid for, and dealing with more legitimate student questions). Then the student will often fail anyway, because you cannot explain in five hours a 30-hour lecture course to someone who really doesn't understand anything.
And then, occasionally (but often enough for it to be a worry) the student decides that having paid his tuition he is entitled to pass the course. And since he hasn't, it must be someone's fault, and therefore he will go through the university complaints procedure (or even sue). And then the lecturer ends up wasting part of their summer (when we probably wanted to be attending conferences, where we promised to give talks which will now be cancelled, thereby annoying colleagues), sorting out some argument that in fact we did everything we reasonably could to help the idiot pass the course. And, very simply, the easiest way to make this argument is to pull out the attendance record. If I can say the student has only been to half the lectures, I won't have to worry about my summer plans being disrupted: the university won't even listen to student arguments that the course was too hard.