To be pedantic, assembly languages do generally have multiple types, if by 'type' we mean 'a set of values disjoint from other sets of values'. For example, x86 has the types integer, floating point, MMX, SSE, and registers of these types cannot be confused for each other. It's just that these classifications/types aren't so useful, and we can't make our own (and perhaps all we really wanted was a distinction between integer and pointer)