Why would my doctor suggest getting botox for an abductor contracture?

Botox. Paralyzes muscles locally. A muscle contracture needs to be relaxed to improve it. Botox works well in this situation.
Relaxation. Botox can help the muscle relax if they are contracted. It can be an effective treatment.
Improve contracture? Actually Botox is indicated for muscle spasticity. If the spasticity persists for a long period of time then a contracture can develop. After this happens Botox is less likely to help, but may be an option prior to surgical release.