Why do I need lumpectomy before mastectomy?

Hi Everyone! At the beginning of February I was diagnosed with stage 1 TNBC, but grade 3 (fast spreading), so my Oncologist recommended chemo before surgery. I did my 4 infusions of Red Devil and just last week completed my 12th infusion of Taxol. In a few weeks I am scheduled to have a lumpectomy and breast reduction. Then, after 3 months I will have a bilateral mastectomy with reconstructive surgery at the same time. At the beginning of my journey, the 2 surgeries seemed to make sense based on the Surgeon and Oncologists reasoning, but now I’m starting to question it more. Honestly I can’t remember what their explanation was (chemo brain!), but as more people ask about it, I’m wondering too. If I am having everything taken off, what is the point of a lumpectomy? Why can’t I just have the one surgery and be done? Has anyone else had a similar treatment plan to mine? I feel like mines all backwards…