There are three things that happen here.
1. You get the job, stay for 1 1/2 - 2 years and realize it is a shit company that is poorly run and you start looking after being there 9 months. The first three months of looking you debate with yourself if you should stick with it or just move on. After 12-14 months, you realize it will never get better and people that work there are there to retire or just don’t know what they are doing. You realize the Japanese culture is so deep in this company and you promise yourself you will never work for another Japanese company again.
2. You have been there so long, the LTI bonuses keep your there and you have no idea what it is like to work in a real company. You will complain about everyone and everything and never do anything about it. You will keep saying you are leaving, but year after year passes and you realize you have been there for 15 years and you know nothing else. You are always jealous of your friends talking about their jobs and always give the same line, “my job is going fine”, when they ask how things are going.
3. You think you are doing a decent job and then one day your manager schedules a meeting with you with a vague subject line and when you walk into the conference room, you are let go for no good reason. They mostly let people go after a year and you would never expect it.
Hope this helps you understand why there are several job openings.