The Gemmorah sets a rule - while saying a Halachah one should mention its [original] source (Megillah 16a):
"אמר רבי אלעזר א"ר חנינא כל האומר דבר בשם אומרו מביא גאולה לעולם שנאמר ותאמר אסתר למלך בשם מרדכי"
And Rabbi Elazar further said that Rabbi Ḥanina said: Whoever reports a saying in the name of he who said it brings redemption to the world.
The Halachot in the Mishnah and the Talmud are said in the name of the Tannayim and the Amorayim themselves (the end of the 2nd Temple), but not their ancestors.
Rambam in his Introduction to the Mishnah says that every Rabbi wrote the Halachot he heard from others to himself in his own collection, but, seemingly, everyone had to include the originator according to the Halachah above.
So, if there was a clear lineage of the Oral Torah tradition, why the Sages never mention their own sources, and it appears as if they "invented" the Halachot themselves?