This is why when my children were little their bedroom floors had to be cleared before they went to bed. I would stand in the doorway and help with directions on where to put things but everything did have a place.
There are loads of threads on the teenagers board where parents will say all teenage bedrooms are like this. Even photos have been posted. They are not all like that. I would be ashamed if mine were.
I shared a room, and a small one at that so there wasn't a lot of space on the floor between mine and my sister's bed. We kept it very tidy but I believe that we didn't have a huge amount of stuff either.
I think when they get as bad as those photos then it becomes harder t know where to start, but they have to start somewhere.