Why did some members of the Borgia Family want to join the clergy?

They knew the advantage of being clergy went far higher than the money they had.

Explanation:

The House of Borgia was one of the leading families in the time of the Italian Renaissance.

They had a Spanish-Aragonese background as a noble family.

They were from Aragon.

Their surname was a toponymic from the town of Borja, then in the Crown of Aragon, in Spain. This meant that their ambitions had not just been to be wealthy but to wield power.

That to wield power would require a lot of people in the clergy to influence the tides in their favor so they had tries for that.