DS graduated HS in 2015, and he was playing HS soccer starting in 8th grade. We're a very small town, and received a waiver from the state association allowing 8th graders to play on JV. However....they could not cut an upperclassman for an 8th grader. He tried out again as a Freshman and was a 'swing' player. Praciced with the varsity 2 days a week, JV 3 days, and played games with JV, unless the Varsity was WAY shorthanded. By the time he was a sophomore, he was full time varsity, and starting. Much to the dismay of some upperclassmen.....
At the start of his Jr Year, they opened our new Jr/Hs, where grades 7-12 were under 1 roof. This allowed teams to field Freshman, JV and Varsity teams, which opened up more opportunities, but there were still cuts.
He also ran winter and spring track for conditioning, and remarkably, our tiny little town was something of a XC and track dynasty, and very successful. But, there were never any cuts for track. If you wanted to join, and put in the work, you were on the team.
So it's really dependent on the sport, the town, the high school, etc. No real cut and dried answer