Hi;
As you said 8 bit are traditional controllers and mother of all controllers. We switch over to 32 bit controllers due to the fact that 8 bit has many disadvantages, like execution speed, peripherals, memory, internal bus interface facility and its speed.
32 bit overcome all the problems or limitation posed by the 8 bit controller. So it is always better to newer technology for updation in technology. We should use all the resources that the technology gives instead of relying on something which is old and have many restriction. but 8 bit technology will never become obsolate as it is the basic tech, we need to understand any further new technology,
Hope I answer your question.