Because then how would one be able to distinguish between multi-dimensional arrays and actual arrays of arrays? They are really not the same thing.
As for what you are trying, you can do this:
julia> repeat([1 2 3], 5)
5×3 Matrix{Int64}:
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
But I suspect that there is something wasteful going on here. By creating an array with many equal rows, you are using up memory without actually storing more information. Do you really need this?