Why did Joseph pray to his Lord to join him with the righteous instead of the prophets, even though he was a prophet?

The prophets are the masters of the righteous. Yusuf's (peace be upon him) supplication to be joined with the righteous includes the prophets. Many of the Salaf interpreted his intention behind "the righteous" to mean his prophetic fathers (peace be upon them), or righteous people in general. Ibn Abbas interpreted Yusuf's supplication as him longing to meet Allah and desiring to be joined with Him and with his fathers among the prophets and the righteous. Al-Alusi mentioned that his request to be joined with the righteous was an act of humility and modesty on his part, especially if "the righteous" referred to his noble fathers: Ya'qub, Ishaq, and Ibrahim (peace be upon them).