Why were Hazrat Yusaf's brothers forgiven?

Hazrat Yusuf forgave his brothers as this was the right thing to do. Allah would not have liked him to carry spite and malice in his heart. Hazrat Yusuf knew that if he forgave them he would be happier and so would Allah also be happy. If he hadn't forgiven them then he would be carrying around a burden and would seek revenge. This is why forgiveness is encouraged in the wonderful religion of Islam.