The main reason why employees leave companies can be on lack of incentives or rather lack of growth. Some of these companies are too rigid to the extent that its workers have less time to spend with family or even time for themselves. Some work six days in a week at at least 10hours daily. Another thing that prompts some workers to seek greener pasture else might be because they are not comfortable with shifts allocated to them, lack of growth within the company like raising in ranks easily like government owned work places. It could also be due to fear, some companies scare there workers with sack and they feel threatened so when better jobs opportunities come they turn to jump on it. Some of this companies also don't have retirement plans like pensions and workers tend to look for pensionable jobs since its hard to save for some during their active working days. Irregular transfers of employees by employers can effect the switching of jobs or people seeking to be independent.
Concerning millenials they tend to give up on eventually everything, they can't withstand even minimal pressures older generations face. There career impatience or overall impatience leads them to been layoff from works or even leave them selves. Although it's a great thing some things are changing in this century like speaking up when there is pressure but dedication, respect towards work shouldn't change