You act as if sending Scraggy to Juniper is like releasing him or giving him the cold shoulder. Just because it hatched from an egg does not give it priority over the others.
Phanpy rejoined Ash's team when he headed into the Battle Frontier.. Just to counterargument that hatchlings do have some priority over others.
Scraggy is very weak and needs the most training. It's also young and looks up to Ash as a parenting figure.
That also gives it priority to others like Snivy, Roggenrola or Tepig in my book, since they have either good moves or a decent amount of gym wins to prove that they're not needed on team for training all the time. Palpitoad, Swadloon and Tranquill are evolved, thus they should be a bit decent already.
Scraggy has none of this, no great moves, hasn't evolved, hasn't had any wins, and has no strength. All the more reason to keep it on the team for now, if I were Ash.
As for the other two: Oshawott has been on the cast and printed its mark on so many episodes that I doubt it's going to be rotated out any time soon. And of course, Pikachu has immunity as well.
But heck, if the moment comes when we see six pokemon on Ash's side and none of them is Scraggy, then call me out. It just seems illogical to me at the moment.
Funny part is I though Turtwig was going to be DP's Star.
Then his Rival's pokemon flipped the tables on us.
Maybe if Shooti's Timburr-evolution keeps on losing, he will release it, and by some odd twist of fate, Ash adopts him into the reserves.
Lol, well, that does happen from time to time!