It's difficult to get into a good Japanese university — entrance exams are competitive. High school students all over the country fill cram schools on weeknights and weekends to prepare.
They go to shrines and pray for academic success. When the big exam day finally comes, many don't make the cut. Students often need to settle for a b-class university or community college.
Many top universities have private elementary and high schools (shougakkou, chuugakkou, koukou). Students that can pay for years of top tier private education are fast-tracked into the university. This represents a two-tied system — it's almost like paying to get into the school.
Once admitted to a Japanese university, students almost always graduate. All that students need to do is pay their tuition and show up occasionally.
University plays an important role in the socialization of youth in Japan. University clubs are all important (virtually every student joins at least one). Whether you join the chess club or rugby club — activities focus on drinking.
University clubs are run much like Japanese companies — they're strictly hierarchical. Senior members of the club run everything. The clubs are considered important preparation for life in a Japanese company. Many university friends establish lifelong business relationships.
To be fair, many Japanese universities have an excellent academic record. Many university students in Japan reach great heights of academic achievement. It's just that if you want to slack and graduate — it's often possible. That's exactly what many Japanese students do.
The primary motivation for students to show up to class and study is company exams. Japanese companies (well aware of the condition of the university system) conduct company exams as part of their new graduate hiring process.
Japanese Companies hire engineers who have never studied engineering, IT staff who've never studied computer science — just as long as the applicant can pass the company aptitude tests. Japanese companies invest heavily in training new recruits.