As seen in the name, Imaginarium has many imaginary properties, especially quantities/size/dimensions and properties derived from those three.
An alternate The Box with different Existence Rank pairs (-1 and -2), went through similar events to our Box. It started as an infinite amount of useless layers, and layers collapsed every OYC until a layer collapsed in the right way to form verses.
However, due to the negative properties of that Box (-1|-2 existence vs 0|1 existence in ours), order and chaos were negative (because order and chaos sum up to a existence rank), leading structures perpendicular to traditional order to form (antiorder) to form.
But what is "perpendicular to order"? Well, it can be described as the imaginary axis of numbers, as it still forms a "structure" yet is a separate axis from real numbers. And indeed, Imaginarium has many imaginary properties.
Why is there no Archverse chain here?
This is because due to Imaginarium's properties, many verses have imaginary dimensionality, as well as imaginary diameter. In order for Verses to properly form, values must be very specific, else either total size will have an inconsistent angle (leads to strange things like negatives containing positives), or absolute value will be static/approach 0 (even worse).
Even if size and dimensionality are habitable, the area around can still wreck havoc with strange properties. This means that outsides of verses may need to be "walled" off.
Due to this requirement, only one type of verse is present, known as the Imaginary-verse.