Historically, there hasn't been a demand for it. Maybe someday, if the sport remains popular worldwide and the funds are available to support it, junior continental championships would be instituted. But then you'd have to find a time in the schedule for them. When do you suggest?
Off the top of my head (I'll look up specifics later if you're interested)
Europeans has been around since 1892
Worlds 1896
Junior Worlds 1976 in its original form
Grand Prix (unified series leading to a final) 1995
Junior Grand Prix 1998
Four Continents 1999
There would never have been a demand for junior continental championships on the basis of parity before Four Continents existed in the first place.
Given that Four Continents serves the whole world except for Europe so that it's always halfway around the world from some participating countries and therefore top skaters from those countries sometimes choose not to participate, it might involve too much expensive travel to attract a full field of junior skaters as well.
And in both continental groups, in any given year the junior ladies might outscore the seniors, at least on technical merit. Especially in Olympic years when top skaters are more likely to skip the continental championships.