Why Do Some Breast Augmentation Results Appear Saggy?

The issue of sagginess has two components.
The first is related to the position of the implant on the chest wall. If the implant is placed low on the chest wall, even if it is in harmony with the skin envelope and nipple position, it will appear to hang too low, or sag.
The second has to do with the position of the nipple relative to the breast mass. If the nipple-areola complex is too low relative to the implant, the nipple appears to be pointing south.
In both cases the situation can be improved by performing a lift in combination with the breast augmentation. In my office, I stand the patient in front of the mirror and let her guide me as to where on the chest wall she wants the implant. Once I know what her ideal implant position is, then I decide whether a lift will help her.
For a link on the importance of implant position, see the link below.

The implants augment the breast shape.  If there is aging before surgery, there will be sagging after surgery.

Thank you for your question. The final breast augmentation result depends on the amount of sagginess, or ptosis, present in the breasts pre-operatively, the surgeon's placement of the implants, and other factors. If the breasts have too great of sag (ptosis) pre-operatively, it may be better to undergo an aug/pexy, which both places implants and lifts the breasts through a mastopexy.

It’s not unusual for patients who have breast hypoplasia
to also have associated breast sag. How this sag is dealt with at the time of
breast augmentation may explain why some women have persistent sag following
this procedure. When this situation arises patients are often willing to make
compromises to avoid scarring. They’re willing to trade scarring for residual
breast sag.

Under these circumstances, breast implants are
occasionally placed on top of the muscle or biplanar breast augmentations are
performed with the implants partially beneath the muscle. This avoids scars
that are associated with breast lift surgery but results in persistent breast
sag.

In other cases breast sag may develop following breast augmentation
surgery. This can occur following pregnancy, breast feeding, weight loss,
weight gain, hormonal replacement, menopause, and normal aging.

It’s important to realize that the type of procedure
performed is dependent upon the patient’s anatomic findings and aesthetic
goals. When these decisions are made a series of tradeoffs
are necessary. In many cases patients are willing to accept persistent breast
sag to avoid scarring.

If you see photos of women with saggy breasts after breast augmentation, then chances are a breast lift may have been needed prior to surgery. While some implants can help lift the breasts to a certain extent, if there is a lot of sagging then a breast lift is necessary. Also, changes can occur after surgery that contribute to sagging, such as weight gain, pregnancy and aging.

The appearance of the breast after augmentation is related to the preoperative look. Therefore, augmentation of a sagging breast leads to a fuller, but still sagging breast.

Some patients are fine with this. They can do their own lift with a great bra, and avoid the scars and expense of a surgical breast lift.

Secondly, placing implants that are too large will create sagging over time. This is especially true of saline implants, which are about 20% heavier than silicone gel devices.