Simply put, if you want to enforce rules around typing in your VM, then you have to build typing rules into your design, and that forces you to try to precisely categorize the kinds of computations your VM can perform with a lot more detail. Beyond having the ability to assign types to everything, it seems to me that a typed VM design must inherently take on more responsibilities than an untyped VM design. It has to enforce a small set of hard constraints, such as making sure that pointer dereferences respect valid address bounds so that the running program can't crash the host VM, but it doesn't really need to care about the types of values or enforcing typing constraints.