Those same rules, for the most part, were in force for 70 years. As the Olympic Games rose to the pre-eminent position in the sports world, to be the goal every athlete aspired to, their staunch defence of pure amateurism drove the culture that kept these rules in place.
It wasn't until the death of American Avery Brundage, president of the International Olympic Committee, in 1975 that serious chinks began to appear in this wall of ideology. Brundage was a hard-line defender of pure amateurism, and with his death, more accommodating voices began to be heard.
I experienced this paradigm shift personally. I was a top level swimmer at the University of Toronto starting in 1979. It was interesting to we athletes when, in 1980, it was announced that amateur athletes could now create trust funds for money earned in sport. It was very limited though, $1-3000 or so could be set aside in trust and not touched until retiring from sport. We had very limited opportunities to earn that money - there was no prize money and advertising opportunities were all directed towards the pro hockey players and such. I don't recall anyone talking about setting up a trust fund then.
But what's interesting is what happened next. In 1980 all amateurs were struggling to get with only meagre government grants, carding, for the very top athletes. Then by 1990, with little change to the rules, there were "amateurs" who seemed to be doing very well, Ben Johnson for example. Amateurs were getting a little ad money, appearance fees were popping up in track especially and corporate sponsorships were becoming available, for the very best high profile athletes. What happened?
It seems to me that the rules didn't change, they just weren't enforced any more. The culture and priorities at the governing body level had changed, and athletes were beginning to enjoy the fruits of their labour financially (the .001% of athletes at the very top anyway). It was all very passive.
Twenty-five years later prize money and appearance fees, corporate sponsorship and advertising opportunities are the norm for the very top swimmers. It's still the barest fraction of what the pros can make, but the "amateurs" are no longer the amateurs Avery Brundage believed in.
And at the Olympics? "Dream Team" professionals, mega-millionaires like Magic Johnson and Sidney Crosby are welcomed into the "amateur" Games. It all happened very fast with little debate.
Whether this is a good thing or a bad thing is a matter of debate.