Why would scar not fill in? (Pohto)

It sounds like you have already tried several treatments for your scar, including CO2 laser, Bellafill, and Alloderm. However, if the scar tissue keeps sinking back down, it's possible that the treatment options you have tried so far may not be effective for your particular case.

You may want to consult with a plastic surgeon or dermatologist who specializes in scar revision. They can evaluate your scar tissue and recommend a treatment plan tailored to your specific needs. Some possible options for treating a sunken scar include:

Fat transfer: In this procedure, fat is removed from another part of your body and injected into the sunken area to fill it out.

Dermal fillers: Dermal fillers like hyaluronic acid can be injected into the sunken area to temporarily plump it up.
Skin grafting: In some cases, a small piece of skin may be removed from another part of your body and transplanted to the sunken area.
Scar excision: In some cases, the best option may be to surgically remove the scar tissue and then close the wound with stitches. This can sometimes result in a better outcome than other treatments, but it will leave a new scar.
It's important to discuss your treatment options with a qualified medical professional who can evaluate your specific case and recommend the most appropriate course of action.

I hope this helps,
best of luck !