Because Hannibal and Will were both in denial about their feelings/need for each other

she cut off her own leg and was waiting for Hannibal to show up.

Fuller says the scene hints at Hannibal surviving the fall, cutting her up, and her clutching the fork to stab him with it when he comes back in the room. wat?

The table is set for 3 people, and one of the chairs is removed and placed in the corner. So the scene is hinting that one of the guests is in a wheelchair (maybe will) and there are multiple guests. And yeah she puts the fork down in her lap which she otherwise wouldn't do in the scenario you described. It is surprising Fuller came out to give his interpretation of the ending though, I thought it was meant to be slightly open-ended.

To go in more detail. There are 3 chairs at the table, but there are also only 3 place settings. The 3 place settings are at the two heads of the table (Hannibal/Bedelia), and the remaining place setting is at the part of the table that has the chair manually removed. The other chair is left at the table without a place setting to tell the viewers that there are specifically 3 guests there, one of which being in a wheelchair.