Obeying the Husband in Islam: Why?
Question

Why is it that when people get married the woman has to do what the man says?
Praise be to Allah.The importance of submitting to Islamic rulings
What the Muslim has to do when he learns the ruling of Islam is to submit to it and believe in it even if he does not know the wisdom behind it. Allah says (interpretation of the meaning): 
“It is not for a believer, man or woman, when Allah and His Messenger have decreed a matter that they should have any option in their decision. And whoever disobeys Allah and His Messenger, he has indeed strayed into a plain error.” [Al-Ahzab 33:36]
He should be certain that there is the utmost wisdom behind all the rulings of Islam, but that wisdom may be hidden and he may not understand it. In that case, he should realize that this is due to his lack of knowledge and the shortcomings of human intellect, which is not free of defects. 
Resolving differences in marriage
When a man and a woman come together in marriage and live together, there are bound to be differences in opinion between them, and one party must have the final say in order to resolve the issue, otherwise the differences will multiply and disputes will increase. So there has to be someone in charge, otherwise the marriage will founder. 
Why should the wife obey her husband in Islam?
Hence Islam made the husband the protector and maintainer of the wife and gave him the responsibility of heading the household, because he is more perfect in rational thinking than her in most cases. This means that it is obligatory for the wife to obey her husband . Allah says (interpretation of the meaning): 
“Men are the protectors and maintainers of women, because Allah has made one of them to excel the other, and because they spend (to support them) from their means” [An-Nisa’ 4:34] 
Among the reasons for that are the following: 

Men are more able to bear this responsibility , just as women are more able than men to take care of the children and the household affairs. So each of them has his or her natural role and position. 
In Islam, men are obliged to spend on their wives ; the wife does not have to work or earn a living . Even if she has an independent income or she becomes rich, the husband is still obliged to spend on her as much as she needs. Because he bears the responsibility of spending, he is made the protector and maintainer of his wife and is put in charge (of the household). 

Hence we see chaos in the societies which go against that: men do not shoulder the responsibility of spending on their wives, and wives are not obliged to obey their husbands; they go out of the home whenever they want and leave the marital nest empty and neglect their children. A woman has to work hard even if that is at the expense of her house and family. 
Rewards and limits of obeying the husband in Islam
We should also take note of the following points: 

The woman will be rewarded by Allah for her obedience to her husband. 
This obedience should not involve disobeying Allah. The Prophet (peace and blessings of Allah be upon him) said: “There is no obedience to any created being if it involves disobedience towards the Creator.” 
Just as the husband has the right to be obeyed, Islam also tells him to treat his wife kindly . Allah says (interpretation of the meaning): 

“And they (women) have rights (over their husbands as regards living expenses) similar (to those of their husbands) over them (as regards obedience and respect) to what is reasonable.” [Al-Baqarah 2:228]
So, the husband should not mistreat or oppress his wife , or issue harsh commands to her. Rather he should deal with her in a wise manner, and tell her to do things which are in her interests, his interests and the interests of the household, in a kind and gentle manner. 
The Prophet (peace and blessings of Allah be upon him) said: “The best of you is the one who is best to his wife, and I am the best of you to my wives.”
And Allah knows best.