The old guard were not spoiled by success the way they are now.
It was a lot tougher back then to make it to the pros, and stay there. There were many fewer teams, and the rosters were a lot smaller. The year the Boys won their first SB, 1971, the roster was only 40. 1959, there were only 12 teams and rosters I think were only like 32. Now there are 34 teams with 53 men each. 12 teams at 32 each is 384. 26 teams in 1971 at 40 each is 1040. 34 teams with 53 each is 1802.
And only the stars in the early 70's did not have to get a job off season. If you were a lineman who was not a starter, you made maybe $10,000 a year. Now while that was not bad wages for 1970, auto workers in Detroit made about twice that- and did not get pounded for 6 months of the year. Also, they realized just how great they had it compared to a lot of people, and just how much of an accomplishment it was to make a pro teams final roster.