In looking at it I don't think physical size is much of a concern anymore. Generally though you can buy two if not three 5 speeds for the cost of the 6 speed. At least used, while probably not as much of a variance new, a lot of that cost is still going to be there.
Weight possibly. I think the 6 speed has about 3-4kg over the 5 speed. Not enough to make a terrible difference. I'd just imagine price and availability.
And while it seems like it's good to a lot of us to have a 6 speed in there. It seems we're in the minority and without real world testing we're not going to know.
A 5 speed is an easy low cost solution, I'm pretty sure that's what drove it, no pun intended.
Personally though I enjoy working on transmissions and vehicles, I can source a 6 speed for a decent price through friends here so when I get my three wheeler, this is definitely going to be something I give a go. Worst case, I hate it and have to convert it back. It'll be a good learning experience either way.
