Utada's fanbase is almost dead, they only appear when she releases a new single or album and disappear very fast.

I think it has to do with Hikki doing almost none promotion for new material. She did tons of promotion for Fantome in TV, but none of the singles released after had TV promotions. And I believe that most of Hikki's fanbase nowadays don't listen to J-pop or Asian music, after her hiatus most of them migrated back to western music, differently of other Jpop fanbases that moved into Kpop.

I believe now that her music is avaiable for streaming many fans might be back, since Hikki's trying to make her music as accessible as she can.