They're not achieving higher runs because 14.1 isn't "the game" anymore.
The new and improved fundamentals are mostly improved in the areas of accuracy on longer shots (or into tighter pockets), and stroke power, both of which are more important in 9-ball (or 10-ball) than in 14.1.
I think if the top 10 players from 50 years ago matched up against the top 10 now in 9-ball, the top 10 now would win easily, party because of greater accuracy and stroke power in today's players. If the same players matched up in 14.1, the players from 50 years ago would win, mostly because of better knowledge of 14.1 patterns, and better touch in manipulating the stack.
The balls are still round and the table's still rectangular, but the game has changed. Today's players have skills more tailored to today's game. Who's "better" is as hard to define as it is moot.
-Andrew