Why didn’t my results meet discussed expectations?

From your photos it does appear that the breasts sit low on the chest wall. It may be that your tissue is too thin for the weight/size of the implants. You may consider adding mesh support and/or smaller implants along with a revision of the breast lift to improve results. I've included a video on mesh that I hope you find helpful.

You did not post your before photos, but based on these, your natural breasts sit somewhat low on your chest and the bases of your breasts cannot be moved. You cannot have high full breasts. Second, with such a heavy implant, your tissue that was previously thinned and stretched cannot hold such weight and is sagging. You would do better going down in size and going with a round implant placed behind the muscle which will give more upper breast fullness and some support to the implant.

It is impossible to say much about your result without preoperative photos. In general, larger breast implants and stretched skin (severe preoperative ptosis) have a tendency to create the result that is shown in these photos. You should wait at least 6 more months for your result to mature and settle and then discuss with your surgeon whether some improvements (fuller upper pole, cleavage, areola lift), can be made using fat grafting and lift revision. Hope this may help.