Research, development... production costs of making what will no doubt be a limited run of essentially bespoke devices (even if they are built using "open" hardware).
There is always a fairly significant amount of time, effort and money spent on bringing a product to market... My guess is that they're just trying to recover these costs. Sadly, in a market that has two well established leaders which are already at significantly lower price points, it is going to be difficult for them to sell many units.
Imagine if Apple/Samsung were selling $500 flagship smartphones... and Google/OnePlus showed up with a $1000 smartphone... because that's pretty much what the Passport folks are attempting to do here
