What does that have to do with implementing a 2D model of a room with movable furniture?
How is paper not accessible? Do people not have note paper? What about junk mail? The last few pages of a book? You can make a scale ruler with any uniform markings.
actually using paper for designing objects, especially complicated objects, is an extremely annoying process. lots of erasing lines causing paper to break, areas with internal complexity requiring sub-diagrams, often causing nesting complexity to blueprints on large projects. It makes it so much harder to simply view and talk about the current state of a design when that means sorting through filing cabinets for revision B12 part A.3.1 only to find the paper has torn. Not to mention making physical carbon copies of things.
It's one thing to draw a rough sketch of a part, and have someone else do the creative effort of turning it into an object. But quite another to specify in exacting detail how that part should be, so that given to several manufactories you would get back parts that are even remotely interchangeable. In that way it's a lot like the difference between a specification for a computer program, and the actual program.
When designing parts I often use pencil and paper when in an initial meeting with stakeholders, to quickly demonstrate ideas. But these sketches are not analogous to the real thing. They simply represent a direction work could be done
This doesn't necessarily apply to every situation, but drawing, cutting out, and positioning paper takes more manual dexterity (and potentially artistic ability) than moving things around on a computer.
Pieces of paper are also likely to shift if you need to move things around frequently.
In a small apartment, surface space could be limited.
