Where I work, managers are mostly promoted from their engineering positions than hired. And it is usually the good ones who get promoted. So whether they end up being good managers or not, they do continue to be good technically. Ours is a big company, so we do have our chaff. We have managers who were good technically, but wanted to have the "easy" life of management or managers who were promoted to management where they shouldn't have been promoted. This group is a minority though and the members of this group usually get sidelined from the people who do actual work.
Also, at least in my company, management life is not completely easy life. Tech is the better life and higher you get in tech, the more you get to go home at a regular time. For many of the managers, they need to work with teams in different countries. There are managers with teams in India and China, having conference calls managing their teams during nights and meetings during the days with their bosses and peers. There is flexibility on when and how you work, but that flexibility works both ways. As a manager you are expected to be available at mornings and evenings beyond the working hours.
