Again, sometimes this is possible (and that is our goal as well). Other times it simply is not. Again, this is nothing against you, but firms have priorities—hiring priorities. They must deal with those priorities, varying partners'/associates' schedules, and outside influences such as OCI, which distract them from our hopeful focus on scheduling everything during the same week.
Firms aren't trying to play hardball when they say they can't do something. It's simply that they are very often juggling five people's schedules, one partner's hiring priority, and their own work duties in order to create time to interview you.