Honestly?
Because back then the budget of the best team was about 120% of the budget of a division 2 team. If liverpool wanted a player from scunthopre they could offer him an extra 10% raise.
Now the budget of the top teams is about 500% what the budgets of the diviison 2 teams are. Chelsea can offer a player from doncaster 8 times what doncaster can.
In the 1950s, Tom Finney and Johnny Haynes stayed their entire career with preston and fulham, these days that doesn't happen. There is a reason why leicester have vardy and mahrez, who were playing semi profesisonal football and nobody wanted while newly promoted forest could go out and buy the england first choice goalkeeper.