If you have an emergency that requires you to divert to an en route alternate and you don't have any approach plates for that airport then you have just doubled the emergency and halved your chances of getting down safely.
I was lucky enough to work for a major long haul airline, (SIA B744), who provided not only all the charts you would need for your route but just about every other chart that you could possibly think of for airports that, under the most unlikely of circumstances, you may have had to land at.
Much cheaper to provide charts that may never be used than to pay up for an aircraft that came to grief because it didn't know where it was going.