I do not know exactly why Peter decided to set up his own factory but, seen that he first tried to find a sub-contractor and only decided to set up his factory late in the project, one very possible reason is that he couldn't find any existing titanium frame manufacturer able to produce the frame for a price low enough to fit into the bike price price paid by backers.

About the choice of titanium : I am pretty sure that this choice is a pure marketing choice, titanium bike have a kind of magic that no other material has, a big part of the communication during the kickstarter campaign was around titanium. The big amount of backers comes from this choice.

The only other choice that could attract as many people would be stainless steel like used for Moulton stainless steel bikes but the stainless steel tubes from Columbus and Reynolds are very expensive, as expensive as high end titanium tubes, and it is not possible to offer a bike at the price of Helix using this king of steel.