Because if we change the Church's teachings on our core natures as human beings, you can just open the lid and flush. That's what liberal Protestant denominations have continually refused to discover.
It's very simple. If the Church continues to insist the first 2000 years were no doubt wrong, but now science is showing how right we can be, it plays right into the hands of the World. Young people today, already evangelized by secularism in our cultures, schools, and media, have learned that religion was just made up by ancient humans anyway. It's just institutions with rules made up by people as they go.
Every time we try to change our teachings to keep up with the latest, it goes nowhere but down. It reinforces what people my age have been taught our whole lives - that when push comes to shove, religion is no different than a club or a sports franchise. You adapt, you change, you make it up as you go. That's because you know it was never real to begin with.
Obviously the World is setting up for the other part of the trap: To deny the 90 ft. idol of the Left is to be Nazi in need of eradication. To stand up against the World will mean persecution and oppression and torture and death. It's not there yet. Heck, it doesn't have to be. By just threatening bad jokes from late night pundits and not getting invited to the best parties at Harvard, we're seeing boat loads of religious leaders jump ship. Already vast numbers of people in the pews have likely done so as well.
After all, we've all been evangelized by the secular for generations now. It has to be taking its toll. But the cardinal's solution is simply suicide for the Church, if that matters at all. It accomplishes nothing to continue to act as if they Church could be wrong about anything. On the other hand, if it wasn't wrong, and the pre-modern Faith was true, such naked accommodation of sin and evil will not just result in nog temporal benefits. It will also result in terrible eternal consequences.
I know where you live—where Satan has his throne. Yet you remain true to my name. You did not renounce your faith in me, not even in the days of Antipas, my faithful witness, who was put to death in your city—where Satan lives.
Nevertheless, I have a few things against you: There are some among you who hold to the teaching of Balaam, who taught Balak to entice the Israelites to sin so that they ate food sacrificed to idols and committed sexual immorality. Likewise, you also have those who hold to the teaching of the Nicolaitans. Repent therefore! Otherwise, I will soon come to you and will fight against them with the sword of my mouth.
A warning for the modern Church.