I think people don't realize that most
KS are not simply to justify the first printing, but to print enough for retail as well and when you sell those to still have money to afford a second printing.
If your
KS costs simply cover your
KS fullfillment, then you have no ability to move forward post-
KS. Some projects, that is ok, but all of these
KS are about getting to retail and being sustainable.
Selling 6k copies to backers doesn't do you a damn thing if you can't sell 30-
40k units at retail later.
I think the point of being used for focus testing is also good as it can really decide depending how the
KS does how heavily they wish to invest post
KS or just cut losses and 'fulfill' and slowly sell out what they have left if they think it won't justify second and third printing later.
This is a relatively good article about production costs and the math which is behind a lot of
KS.
https://blog.foxtrotgames.com/2016/02/24/kickstarter-cash-flow-profit/