From my own personal standpoint, as much as I enjoy her experimental work, I feel like I can understand why she went with a more mainstream sound. I don't know if this is a good example but oh well, here goes.

Say for example, some guy just graduated college and he has this crazy unconventional look. After doing interviews with several different employers, he may potentially be hired by this one law firm. Now, if the guy wants to get ahead in life, he is going to have to change his look to be more "acceptable" by the general population. Only after he gains a reputation of being a really good worker can he go back to being unconventional looking.

That's what I feel Utada is doing. She is getting herself noticed by the general public by doing something a bit more mainstream. After she has people's attention, she can then do something a bit different and more people will listen to it because they know of her. Don't forget that her breakout album in Japan wasn't an experimental album. The experimental stuff came out after she had garnered lots of attention.