1) Because to secure the job career [sounds good but MBA from top univ is still preferable for breakthrough to senior mgmt, partly due to networking obtained during the course of study]
2) Salary factor [depends on which technical field you plan to specialise in. As you are already a engineer, next may be to set up own firm, or to tender for project? All these requires networking. If for satisfaction, it is entirely plausible to go for it]
3) Satisfaction [The latter point 2]
4) Migrate to other country [It opens door to big corporation, score some cekap migration scores, but then again, it depends on what you are pursuing in life (settle down here, or becoming a global citizen].
5) or it is own dream to teach people or passion in endless learning curve. [IMO, this would be the best of all the options listed]

As i know everyone have own dream and desire, so would you like to share your thoughts or opinion.

Studying up to PhD is a passion more than a commitment to fulfill esoteric need or to cover physiological needs (money, fame, migration and other hygienic factors).
Not only it will take up a chunk of your time (3 years to beyond) but it is a particular drain on one's finances too. Consider the need to take care of worldly needs (family, spouse, children, chasing for financial independence, etc) before embarking.
Ultimately learning does not stop when one hits PhD. Plenty of stuffs to be discovered post doctoral.

This post has been edited by SevenTwentyOne: Apr 8 2019, 09:30 AM