>>1878873Short answer:
On a 2x4 you either get narrowly spaced racing gear or wide spaced touring gears ( or something in between ). On a 2x12 you can get both.
Longer answer - people were, generally, fitter, lighter and less fussy about what they were doing. Unlike today, 'race bike' was a bike for racing and you dealt with it. The current generation of people spoiled by "fix by throwing money at it" wasn't born yet.
Moreover, Technology wasn't yet up to the task. Up to the middle 2000 there was one extra cog added to the rear cluster every decade, as technology progressed. In the 50s it was 2x4, sixties 2x5, seventies 2x6 and so on. As noted above, when you have 5 gears to choose from, you are making tradeoffs by necessity. If you wanted to race, than that tradeoff was 13-21 cluster, 52-42 rings at that was already 'high range', because a decade before it would be 14-22 and 52-48.
But if you wanted high range, pic-rel - it was widely available.
