Well, people age, and so do the their relationship with the public and their creative output. What Utada is doing what fits her nowadays, Namie wasn't really into the whole popstar life thing for a while, Ayu is taking her time after almost 2 decades of nonstop releases and groups are tricky to keep around for long...
What really bothers me in a way it's the lack of soloists who become cultural phenomenons and icons... We had Kyary Pamyu Pamyu, who, let's be fair, it's more noticed due to her visuals than she is for her music (and I'm saying this as someone who actually does like her music) and groups like AKB48, but I'm not really into groups.
But I guess this is jpop's natural cycle in a way? An era filled with idols groups and another one filled with soloists with strong personality. I just wanted someone who actually shake things up a little like Ayu Hikki, Namie, Shiina, and gosh, even Koda did.
Until there... Vickeblanka and Reol are releasing some pretty interesting music.