What are some typical reasons why employees quit their jobs?

Bad Boss, Yes, Yes, Yes.....
Many friends of mine said that they were "leave their bosses - not their jobs" or "leave managers not companies"...in the end mostly due to a manager issue. Usually bad boss behaviors include: Bullying ,Incompetence , Harassment and discrimination ,Inadequate compensation and Not respecting legal rights. They usually create fear in the workplace and give a high pressure to employees and left them no choice to leave the company.

I agree, probably, bad boss/manager is the first reason we have to think of.

No promotion - no benefit - no managerial system.

Employee leaves the leader not the company. If employee doesn't believe in belief of leader and doesn't find their personal values fit in company value, then it is not surprising that they won't follow their leader.

Every year, HR consultancy publish this list for Vietnamese employees
From an employer perspective: I never heard the frank and straight forward You are bad boss. It takes courage to say that!
Here is a little list of typical reasons that proved a lie 70% of the time.
I am opening my own company
I am going for study (abroad)
My mother want me to go Vung Tau
Insurance is not a business for a lady, my family say
I plan to have a family so I must stop working...

Tough for the boss to get the truth!