Because the pope is the legitimate successor to st Peter, and he is the vicar of Christ. Being a bishop and denying the pope's legitimate authority publicly is a huge sin akin to denying the entirety of your faith.

You are correct insofar as Catholicism, which is why Catholics are painted into a corner. I guess there's a theory that Pope Francis wasn't legitimately elected, but the process is literally a cabal of elderly men making smoke signals to the world so there is no such thing as transparency or legitimacy involved as we know it.

And it cracks me up that atheists and protestants are so invested in this process when they deny the entirety of it. It's almost like you guys just can't escape the fact that God exists and this is his church. You're drawn to it whether you acknowledge it or not

Conflating prominence with truth is a mistake.