There're so many reasons...And in India we are still running over single cylinder...he he....
- The days when motorcycle engine were getting popular, they believed, there's no replacement for displacement
- They were still evolving
- Technology was just evolving
But today, things have come way too far from beginning of 20th century. Something to think about...
Yezdi - 250cc single 2 stroke produced 16 Hp yielding 20-22 Kmpl, while CBR 250R - 250cc single 4 stroke produced 25Hp yielding 33 Kmpl...atleast
They will do it soon; this is why we see...God knows when will our own Indian manufacturers produce their own design of theirs ??
Hero - EBR partnership
BAL - KTM partnership
TVS - Triumph (though rumor) partnership
Escorts has been dead anyway!!!
This is the advantage of early start that can help to evolve as one identity.
For instance, Yamaha's first motorcycle was a copy from Germany, while Honda started everything from ground zero. Yamaha was the last Japanese company to join the motorcycle manufacturing bandwagon, while Honda the first.