Possibly because that's quite user-hostile? I may not be in a position to generate a new password and save it on a given arbitrary login to the site.
Fundamentally, this isn't a high-risk situation. If the password controlled something vital, then sure, force the reset on everyone. But what's the worst someone can do with my Kickstarter credentials? They certainly can't spend any of my money, that requires my Amazon password as well.
Also, they say that "For pledges to projects outside of the US, we store the last four digits and expiration dates for credit cards."
Isn't that the information that resulted in Amazon and Apple accounts being compromised last year? Perhaps those two have fixed their procedures to prevent that from happening again, but other companies may not have been pro-active. And even if proper procedures are in place, all it takes is one little screw-up.
Fundamentally, this isn't a high-risk situation. If the password controlled something vital, then sure, force the reset on everyone. But what's the worst someone can do with my Kickstarter credentials? They certainly can't spend any of my money, that requires my Amazon password as well.