Why Does Amazon Cancel An Entire Order When You Just Want To Remove One Item?

I ordered some supplements plus an electric heated throw blanket. Or so I thought. I was looking at so many blankets after searching for a heated throw that I didn’t catch that the one I ordered was a non-electric fleece throw. So I wanted to cancel it because I have enough blankets as it is. I wanted the heated throw to take with me to chemo treatments due to getting chilled this last time so bad that the nurse brought 3 warmed blankets to put on me including wrapping around my shoulders and upper back. I guess they need to cut back on the meds or something, they added Pepcid and I think it overloaded my liver or interacted with everything else.

Anyway I just wanted to remove that one item, the blanket, and hit the EDIT button and removed it. Looked today and they cancelled the entire order.