Mito isn't even the most popular NijiJP and has basically no relevance in the west, this is a pity nomination or a purposeful campaign by Nijikeks, though honestly sisters would've nominated Vox if they campaigned so it's likely a pity thing by filian to save face.Legitimate question, has Tsukino Mito done anything influential this year, or did they just google "nijisanji female vtuber jp"?
FWMC is likely the same, they aren't particularly more popular than any of the other HoloENs and this year was pretty shit for them with them getting a ton of antis and hate.
As an awards show Filian definitely wants the validation of being recognized or even sponsored by the big boys, which will most likely happen with Brave trying to take over all facets of vtubing, having the corpos on her side legitimizes her event though I will also lead to inevitable rigging of the vote (if it isn't already).