A - Thanks for the question! I know this is a point of confusion for many. I hope I can adequately explain the reasoning behind the decision, but let me first point out something else. Don't think the Church isn't doing those other more important things, just because it issues decisions such as these.
The Church hierarchy has a huge responsibility to lead God's people and part of that is to help direct us in the worship of God. Some parts of our liturgy are changeable and some are not. In those parts that are changeable, we might think that it is un-important in the grand scheme of things to address such small issues. But, if we have the eyes to see it, the liturgy is one of the most important things we will ever do and doing it well is extremely important to everything else we do, because that is where our power comes from (God's grace). So, while in this particular instance we might think that we should be focusing on feeding the poor or helping victims of AIDS, let us not think it is not important at all - because it is.
Now, why did the Church makee this change? For a couple of reasons.
1 - The name Yahweh is actually a guess for the name of God based on the Hebrew YHWH. Hebrew is a language without vowels and the vowels must be inferred from the context. In other words, we don't know for certain how to say or write the name correctly - even in Hebrew. In fact, orthodox Jews and ancient Jews would never say the name of God, for fear of doing so incorrectly, because they do not want to accidentally blaspheme God's name. This is why you will find the name "God" spelled "G-d" by some Jews today. Rather they call God by some other name, such as Adonai - which means lord or master.
This ancient practice of avoiding the attempt to pronounce God's name also has Christian roots. Recently, we got away from these roots. Look in your Bible and you will find the word "LORD" with all caps. This is where the name of God is found. Where you find the name as a proper name "Lord" - is where Adonai is found in the Hebrew text. We also get the name Jehovah, from the English translated Bibles that named God as JHVH.
So, there has been a wider use of the name of God, YHWH, that has slowly (and then more quickly recently) started to be used in the songs we sing in Mass. Because we want to have reverance for the name of God, the Vatican has asked that we return to our roots. We ought to think of it this way, rather than them thinking that they have taken something from us. It is an attempt to reverance the name of God.
2 - This will be seen as a step of reconciliation toward our Jewish neighbors. We are showing a sign of respect to both our own tradition and their tradition as well. Though the Vatican did not mention this motive, we can guess it played a part in the decision.
3 - The name of God is not just an identifier for the spirit in the sky. A name means much more, esp. in the Biblical times. Think of John 8:58 - Jesus appropriates the divine name "I AM" to Himself, and the Jews knew that He was proclaiming His divinity and therefore they tried to kill him. This is what the Catechism says about the name of Jesus:
2666 But the one name that contains everything is the one that the Son of God received in his incarnation: JESUS. The divine name may not be spoken by human lips, but by assuming our humanity The Word of God hands it over to us and we can invoke it: "Jesus," "YHWH saves." The name "Jesus" contains all: God and man and the whole economy of creation and salvation. To pray "Jesus" is to invoke him and to call him within us. His name is the only one that contains the presence it signifies. Jesus is the Risen One, and whoever invokes the name of Jesus is welcoming the Son of God who loved him and who gave himself up for him.In the bible, to name a thing, or especially a person, is only done by someone who know what that thing/person is, where its destiny lies, and why it is. Therefore, God names man. Man names creatures (in Genesis). God gives a new name to Abram, Isaac, Peter, etc. Parents share this responsibility by naming their children.
So, when we pray "in the name of Jesus" we can only do so because Christ first united us to Himself. This is because prayer in His name, is always a prayer in and through the Holy Spirit. It is a call to receive His Spirit, which is the fullfillment of all we truly long for. But, it comes true only through a knowledge of the purpose of His name.
Knowing this, we can understand that the name of God is not just any name among others. It is THE name and our reverance for it should come at all times.
I hope this helps to understand why the Vatican made this change.
"at the name of Jesus every knee should bend, of those in heaven and on earth and under the earth" - Phil 2:10