Given that these are the 1.0 dungeons it could well be that when they were originally developed they weren't developed with hard modes in mind -- maybe these particular maps, for whatever technical reasons I don't understand -- don't have the ability/space/room/requirements to be expanded on. I'm pretty sure the 2.0 dungeons, when created, already had the different routes and areas created, or at least catered for, but they were just blocked off.

Adding on to the 1.0 dungeons could just be too much work!

Could be wrong though.