Because... well, just read the A/N at the bottom.
Albus sat in the Owlery, gripping a letter. He still wasn't sure he was going to send it.
The door opened. "Oh, hi," Scorpius Malfoy said.
Albus nodded.
Scorpius found his owl and stared at it for a long moment. Then he too sat down. "You're in Slytherin," he announced.
"You're in Gryffindor," Albus responded.
"Think they'd notice if we switched places?"
"Probably." Albus sighed. "That to your dad?"
"Yeah. Yours?"
"Yeah. How about… on the count of three we just send them?"
Scorpius gulped. "They'll find out at some point."
Two owls flew off into the night sky together.
Unconcsiously, I realized today, I've been trying to work out this friendship for a long time. What would prompt Albus Potter, a Gryffindor, and Scorpius Malfoy, a Slytherin, to become friends? Would they become friends? Or would Rose have to convince them to settle their differences.
And then I read a fic today where Albus was in Slytherin and after deciding that Scorpius would then be in Gryffindor, everything suddenly just made sense to me. They're both outcasted, they're both worried about how their fathers would react.
I still need to think about this some more. I don't know if I agree with it. I don't know what JKR was thinking. But, if Scorpius was in Gryffindor, and Albus was in Slytherin, than that's how it would happen :)
~writergal24