It seems that in higher education, some instructors either do not care at all whether students attend, and others care minimally (often resulting in a 1-5% attendance grade or tie-breaker rule).
However there are also many instructors who seem to feel very, very strongly about attendance, and take it upon themselves to enforce this in various ways.
For instance, I was shocked by a recent question claiming that 15% of the grade would be lost for missing 2 lectures - according to the question author, the class meets so frequently that this would constitute missing less than 3% of the lectures! While this seems like an extreme case, it seems like it's not uncommon to find professors who may deduct 10% or so for missing a small fraction of lectures.
Why are these professors so preoccupied with making students attend? If attendance is so crucial to doing well in the class, wouldn't the students who don't attend do poorly in the exams anyway? Why additionally punish those students who did not attend, but did well regardless?
Let me start off by saying that it is very unlikely that attendance requirement is purely to protect the professor's ego, as one comment suggested. Any serious educator would understand that the goal of education is not so that the students become increasingly reliant upon the education system. Rather, the goal is to produce students that are increasingly independent, critical, and confident in their own reasoning. If I were a professor, I would be glad that the student can succeed without my help, rather than the other way around. To punish a student for being able to succeed without the help of lectures is simply contradictory to the goal of education.
With that being said, here are some more plausible reasons:
- The class is discussion based. This is quite straightforward: if you don't attend the class, then you do not learn. The in-class learning experience cannot be compensated by self-study, and exams may not be an ideal measure of such experience.
- The class meets very infrequently. There are certain classes that meet only once per week. Missing one class means missing a significant amount of work. A related example is science lab requirement. In my undergrad institute missing one lab (without advanced notice) means that you automatically fail the class.
- The lectures contain information not otherwise (easily) available. This is more relevant for higher-level classes, where there are no standard textbook and the way the professor teaches the material may be unique. The professor may want to make sure that students attend lectures to get the information they need.
- Culture. In some culture regular attendance is associated with deference to the system and/or the lecturer.
One finally note: contrary to what OP stated in the question, it is my personal experience (in the US) that very few professors would deduct a significant amount of points due to a lack of attendance. Instead the focus, if there is any, is usually on participation of class activity (which, of course, can only be fulfilled if you attend the class). What OP have described seems like rare exceptions rather than the rule.