Titanium is hard to work with. If you want to shape a fork and not use tubing you need to hydroform it but titanium has a tendency to crack when shaping it. It used to be pretty damn difficult up until very recently (2012). There are a few companies that do build custom titanium forks but in most cases carbon fibre is simply more cost-effective.

Maybe we will see some more companies start offerering titanium forks but it will stay a bit of a rare sight.