1. Question: Why don’t we discontinue reading from the Torah or Megilas Koheles or Shir Hashirim on Shabbos just as we don’t blow shofar or read Megilas Esther on Shabbos?
A. The reason why we don’t blow shofar or read megillah on Shabbos is because of a rabbinic enactment that if there is no eruv one might carry his shofar or megila four amos or more in the public domain in order to practice in front of a sage, who is an expert in the field.
B. The obligation of reading the Torah on every Shabbos, as well as reading the Megilla of Koheles on the Shabbos of Sukkos and Shir Hashirim on the Shabbos of Pesach is an obligation on the tzibur, the entire community.
C. Reading Megillas Esther and blowing shofar is an obligation on the individual.
Answer: If the obligation is incumbent on the congregation then there was no decree to discontinue the mitzva on Shabbos since the person doing it is probably and expert or trained enough to be sure not to carry the items in the public domain to practice. But an obligation on an individual, even if most of the time is done for them in a group, might still have various individuals try to fulfill the mitzvah themselves and therefore might practice in front of a rabbi beforehand to be sure they know what they are doing and so might come o care in the public domain on Shabbos (See Dirshu Mishna Berura 588:5:13:17).