Hi Berry
"My question is why not use biscuit joinery?"
Because we all have kids that get mad sometimes and the biscuit can't take it.
It's just a butt to butt joint so to speak with a spline that holds it as one.
Once the glue joint moves that's it,and it's going to fail, unlike mortise & tenon, it's hard to break the glue joint,because of the size and the amt.of glue use on this type of joint.
Bj