The question was "in the seventies". To understand where we are today, it helps to go back in time and understand the context.
Back in the sixties, most bikes were singles or twins. Twins cost more to manufacture but potentially theu could make more power. That was the time that Honda decided to enter road racing and knew that they couldn't produce a Manx Norton copy and expect to win so they needed a more suitable place to start and that with small motors.
We all know that there are two ways to increase power: raise efficiency and raise revs. Norton and AJS already had efficiency as high as it ad ever been and revs could only rise so far before you hit a wall. You can shorten teh stroke and widen the bore to get revs up and that helps, but at sometime, the only way to get revs up is to use more smaller cylinders and that's the way that Honda went.
To begin with they made 125 twins and 4 cylinder 250s and eventually had a 50cc twin, 5 cylinder 125 and a 6 cylinder 250 and 350. That as great for race bikes but no one was going to pay millions of dollars or pounds to get a 22,000 rpm twin or 18,000 rpm 6 for the street.
Honda were not alone, there were others following the same direction, but they were best at exploiting the engineering. late in the sixties they came up with the CB750 and somehow managed to offer it at a reasonable price. British and Euro manufacturers could not compete with that. They made twins and singles and that what most of bought. Who needed 10000 rpms and not many of us could afford one. Then they came up with the 500 and then CB350F at prices no one else could compete with and a new market opened up in the seventies for well designed higher revving 4s.
A longer stroke tends to generate torque lower down the rev range, so we say that twins are more torquey than fours but that's not necessarily true, but they do tend to make power at lower revs and those longer strokes do create larger turning force (torque).
Most of us continued to ride and race simpler twins and singles, but over time the advantages were eroded and eliminated the advantages of those simpler motors. Twins started to rev as high as the 4's and we learned that twins of the same size as a 4 were cheaper to buy and maintain and ran just fine. 4's were faster but tended to rev more. By the mid sixties the old Norton and Matchless singles were passed by fours and 2 strokes and that clock is not about to get turned back.
The seventies were a time of huge change - culturally as well as what was available in the marketplace. Back then, twins were cheap fun if we're talking CB350/360 and fast fun if we're talking Norton, Triumph, Laverda BMW etc Honda sold a gazillion CB350s as cheap fun. Not as a serious million mile motorcycle, but as something fun and cheap to buy and own. They built a whole new market.
4's appealed to people that read race reports and liked technology, so that was another emerging market.
Today, most bikes are way too fast and have more capability that most of us will ever dream of knowing what to do with, but back in the seventies the world was different place.
I grew up in that era, so for me a big twin is the only way to go for a cafe racer because it captures more of the era, IMHO and is a better match to how we really ride.
