Earlier quoted context omitted.
This is interesting I did a bit of Googling, I guess it varies by sport quite a bit. https://www.post-gazette.com/sports/around-the-league-nfl/20... Some sports, most coaches came from players, but the NFL notably does not.
"Most coaches came fro players" is very different from "players are expected to become coaches". I can't think of any sport where players are expected to become coaches.
In amateur sports it's common. E.g. in rowing, cycling, fencing, cross country skiing, etc., people are generally expected to coach at some point. Albeit usually while they're doing the sport, and not necessarily as their primary careers.