Why do idols pick other company idols as ideal types?

All of ELF knows that Heechul adores Wonder Girls' Sohee. Recently, Big Bang's G-Dragon picked Yoona as his ideal type.
Before, he also commented that f(x)'s Sulli was very cute on stage. This has many fans wondering why idols don't pick girls from their own company as their ideal types and pick girls from rival companies instead.

YG Entertainment has 2NE1, and SM Entertainment has Girls' Generation and f(x). Heechul and G-Dragon could have very well picked girls from their own company. However, many said the reason that they don't pick the girls from their own company is that they are too close to the girls, and that they look at each other as family, not as datable subjects.