It's the typical surge when a character is added Fate Grand/Order
well, that and the redesign for her and passion lip corrected the major problems with the two of them, that being the needless, pointless fanservicey outfits.
Mel seems quite popular lately; has something happened of which I am unaware to make it so?
It actually has more to do with the CCC collab event's story and how much exposition they had on Melt. Basically everyone ended up falling in love with her and started crying when they saw her story.