Mattan Toroseinu is what haShem did, and since haShem had planned to perform Mattan Toroseinu on Sivvon 6th, hence the fact that Moshe postponed it by 1 day to Sivvon 7th, notwithstanding:- We commemorate Mattan Toroseinu on haShem’s intended date of Sivvon 6th.
Kabbolas haToroh is what we are supposed to do every day as we say in Shema:- haYom Al Levoveicho.
Since Shovu’os is a commemoration of wht haShem performed, all our prayers {with exception of 1 Piyyut in Mussof by Oz Shesh Me’os etc.} do not mention Kabbolas haToroh but Mattan Toroh.