Query about slang "scootch"-- Why -ch?

[Dale Coye]

Jim Stalker mentioned the Politeness Principle-- what comes to mind for me is
something like a Baby Talk Principle or the Talking Cute Principle--when
talking to a little kid or when Cuteness is a factor add a lot of SH and CH
sounds.   Kitchey-kitchey-coo comes to mind. And a normal utterance like "What have
you got there?" becomes for some who are afflicted with the Cutes (as in
talking to a dog for example) "Whush shoo got dere"...

Dale Coye
Wilton NH