My Protestant boyfriend recently told me that he struggled with apostolic succession because he didn’t understand why the pope didn’t choose his successor. He felt that true succession was compromised by the cardinals and other clergy making the choice (therefore, popes after Peter don’t have the original authority of the office, and the Catholic Church isn’t necessarily the same church Christ founded). Though I can see how it would be problematic for the pope to make the choice, I don’t know what the Church’s reasoning was for this.
Your boyfriend’s argument is a novel one and certainly is weaker than that of a Protestant who objected on the grounds that Jesus himself doesn’t directly choose each pope.
Theoretically, I would imagine that there is nothing that intrinsically inhibits the Church from allowing each pope to choose his own successor. Had the Church chosen to do it that way, it likely could have been done that way. Instead the Church chose another method, one it deems to be more prudent.
What your boyfriend should try to understand is that the Catholic Church is an incarnational Church, the product of both divine creation and human organization. One consequence of this is that even divinely-appointed offices such as that of pope are subject to being regulated by human mandate. Christ gave us for his Church all that is necessary but expects the Church to do all that is humanly possible to safeguard and bring to fruition the gifts he has given.