1.) Theres too few of them, you only have 3 spots to fil but 5 people to choose from and if you want a party of cool likeable characters you're shit out of luck.
2.) They are overly integrated into the experience. Too much work and detail has gone into making the characters.
3.) #2 is why we have #1
4.) If you think there will be more companions you will be sorely disapointed.