I am an avid Huddy supporter, as are many people, and if they're not, they support another House type relationship - House and Cameron, House and Wilson, just House and someone.
Because of this, Stacy often gets overlooked, since she was the only one who actually won House over. People don't want her to come back because of their desire for Huddy or Hameron or Hilson to occur.
But what about all the great things Stacy actually did bring to the show in the first and second season?
Personally, I really liked her character and the things that she brought out in House's character.
Because of Stacy, we were able to see the soft side in House that, in those first seasons, we rarely got to see. She brought out a different kind of humor in him that was really fun to watch.
She was also a friend to Cuddy, which is something that we haven't seen since she left. Sure Cuddy and House and Wilson are friends, but Stacy was kind of that girlfriend character that sought advice from Cuddy when she didn't know what to do about House. That also triggered an interesting bit of Cuddy's character in the beginning.