Leading into the roster decisions, Scally had barely played in ~3 months for 'gladbach after a brutal run of form heading into the holidays. He recently got a start due to a red card, played well enough for a second cameo, but played himself back to the bench.
I get he had a hot start to his professional career, but I'm not sure the 'most/best minutes of any RB' is remotely close to reality.
He's still 19 in the Bundesliga though, not a bad spot to be as a professional.
Edit: I'm gonna add, this isn't necessarily the worst thing in the world. He was brought in as a long-term prospect for BM, he got thrown into the fire before they ever expected he would need to be due to injuries, and he responded well. But unfortunately, he's going through the growing pains of a teenager playing in one of the most high-pressure stages in the world. He'll be fine in the long-run, but I don't think his exclusion was an error and it was probably wise he's not being considered for the national team at the moment.