1. To give their confidence a boost.
2. To look younger and perkier.
3. To have a larger, fuller, rounder breast (some women are "cursed" with lumpy, deformed or tuberous breasts which are considered by many to be unattractive).
4. To increase their chances of attracting a man.
5. To boost their career (frankly I think that's a false assumption unless you work in the porn industry or adult entertainment).
Indeed many of the reasons will likely go hand-in-hand with the same reasons people provide when getting liposuction or their stomach stapled.
The breast implant industry these days puts more emphasis on the words "breast augmentation", meaning they're not always doing implants but simply they're just augmenting them to look better. Depending on the type of breasts and its problems implants will likely be part of the "solution". Its also better Public Relations because breast implants have developed a bad reputation over the years.
Feminists have often been opposed to breast implants and the idea of women bowing down to a patriarchal sense of beauty. Here's a number of articles on that topic:
The Beauty Myth
Beauty and the Breast
The History of the Bra and Breasts
So thats the female perspective in a nutshell. Don't get breast implants because you're beautiful and you shouldn't need them because you're beautiful anyway.
But from a male perspective I have TWO schools of thought on this situation.
ONE: I agree with the feminists. I don't think women should get breast implants just to satisfy outrageous male standards of beauty. The back pains alone from will cause you to want to get them removed in your later years anyway.
TWO: There will be exceptions and they are as follows: People who have had breast cancer and want to look normal again; People who are seriously depressed about their looks and want to do something about it (no amount of exercise will change the shape of your breasts); Males who have had sex changes (I've noticed the males tend to go for the DD size and take breast implants to the extreme in an effort to over compensate).
Thus women who look normal, and have good looking/normal/fine breasts already shouldn't be rushing out just to make them BIGGER. That to me is morally wrong.
I also have to wonder if we place too much emphasis on breasts period. Some guys are more into ass or legs and don't give a damn about breast size or shape. There are those of us like Russ Meyer who are obsessed with breast size, but Russ Meyer is the exception rather than the norm.
"Its not the size of the breast that matters to men, its how a woman uses them."