1. You didn’t get enough product. 
Honestly, this is probably the biggest culprit of all, and usually has to do with budget constraints. A lot of people prefer to stick within a certain budget-range for their treatment (which is completely understandable), but the dollar-amount they have in mind may not correlate appropriately to their needed dosage. In the event that you cannot afford to fully treat all of your desired areas, it is better to appropriately treat one area then try to stretch the same amount of product for three areas. Quantity equals longevity, and the smaller the dose — the quicker it will dissipate.
2. You have a high metabolism. 
Some people metabolize injections very quickly, and no matter what — their metabolisms don’t allow for the usual result-longevity. (These are usually people who are exercise A LOT.)
3. You may have developed a resistance to the product / you are in the small minority of non-responders. 
If you have been getting large doses of tox* for a long time, it is possible (although rare!) to build-up a resistance to the product. There is also a small subset of people who just don’t respond to the product at all. Unfortunately, this means that no matter how much product is used — your muscles will not respond as desired.
4. You want to retain some movement with your treatment. 
If you are one of those people that likes a more “natural” look with some remaining movement, you will need more frequent maintenance. Smaller quantities of product are used in these scenarios to allow the muscles to still have some movement, and the smaller the dose — the quicker it will wear off.

Please know that it is NORMAL for some movement to gradually return 2-months after your treatment. By the 3-month mark, you will likely have full return of muscle contractions.
* In our office, we use the catch-all term “tox” to refer to all of the neuromodulators; Botox, Dysport, Xeomin, Jeuveau, etc.