Why is there no explicit data-typing in CORBA CDR?

What will be an ideal response?

The use of data-typing produces costs in space and time. The space costs are due to the extra type information in the marshalled form (see for example the Java serialized form). The performance cost is due to the need to interpret the type information and take appropriate action.
The RMI protocol for which CDR is designed is used in a situation in which the target and the invoker know what type to expect in the messages carrying its arguments and results. Therefore type information is redundant. It is of course possible to build type descriptors on top of CDR, for example by using simple strings.