Because in the process of acknowleding this truth you also acknowledged that oral transmission is not as accurate. It is very straightforward to see that oral transmission not being of like accuracy would not be held in as high esteem. Thus, in your honesty you acknowledged that one of the legs of your three legged stool "tradition" is not equal to that of Scripture. IOW, you stool is "falling over".
WM: Why would the opinions of these theologians have any greater weight than the opinions of theologians who came even later?
An: Because they were nearer to the source of the teachings of Christ, both written down and not.
It may not have occurred to you, but proximity does not guarantee insight or understanding. A good example would be the creation of a hierarchy, or the mistaken belief in transubstantiation.
Another way to look at the issue of proximity would be in the work place. I might interview two different people for a position. The first candidate having been with us for 20 years and the second for just 5 years. The first candidate may have stayed stuck in his 1st year throughout his 20 years, never growing or maturing, The 2nd candidate may have had 5 years of different experience and because of it grown and matured. Whom do you hire for the position?
If these early theologians only have proximity going for them then why should they be taken anymore seriously than those who came later?
The teachings of the fathers of the Church are adequately recorded and available to us. We have no problem accessing the Holy Tradition today. The unreliability of the oral transmission has been overcome. Imagine that.
proximity does not guarantee insight or understanding
Well, no, it does not. For example, Judas was among the Apostles, and the Eleven themselves often showed lack of understanding. The Church did a lot of work to harmonize and sort out the memories of Jesus before it could arrive at the complete and accurate picture of the Christian Faith. However, by the time the New Testament got sorted out, the Deposit of Faith was free from aberration. At least, if you believe in the inerrancy of the Scripture like I do, you have to believe that.