At least some legendary sports teams, more specifically the 1980 Olympic Hockey Team, pretty much had the same crew until the end and thus a level of trust and harmony was created.
One reason you don't see much of that anymore is the almighty dollar. Player are signing elsewhere for bigger paychecks. Back in the 70's & before, it was common & often necessary for players to work in the offseason to support there families.
The salaries were nowhere near what they are today in respect for that period of time.