They were waiting for the diecasting molds to get made.... Time consuming..
But I think the real reason was they were not sure they could sell enough units to amortize the cost of the molds.
Something like that, yes. They, for several reasons, had reservations as whether or not the bike would sell as expected, so due to cost of die cast tooling,they held back until
sales took off. They were concerned that the new car they were developing at the time was too close in price to that of the bike, which
seemed to make the bike a lesser value. Another concern was that the 750 might somehow be viewed as anti social and wreck their image, you meet the nicest people campaign vs.a new superbike the likes of which nobody ever saw before. Most notably, the company was nervous about the US government laws at the time concerning vehicle safety, worried
that there might be problems with "Ralph Nader" types, because they had the same type problems with the japanese government when
the 750 was in developement..........(source "Honda Motorcycles", by
Aaron P. Frank and according to Mr. Hansen.) The way I understand it...
Sandcast was the conservative approach amid uncertainty. And there's probably more to it than that IMHO. And PLEASE correct if any of my information is not accurate.