Two simple arguments for why Church doctrine will not change
1) The Spiritual Explanation: The Church was founded by Christ, who is God, and is protected by the Holy Spirit, who is also God. Its magisterial pronouncements through councils united to the pope and (rarely) through the pope are guaranteed by the Spirit to be true. If the Church were to change, it would require God to change his mind. But that's ridiculous. Ergo, the Church isn't going to change its teaching with the new pope.
2) The Political Explanation: The Church is merely a collection of men trying to keep power. These men have whatever claim to power that they do have because they believe that #1 is true, and lots of other people believe #1 is true. If they changed Church teachings, it would show #1 to be false, therefore destroying the power of the Church. We'd become Episcopalians in a hurry. No one wants that. Therefore, the Church isn't going to change its teaching with the new pope.