Answer :If there are more general purpose registers the program writing process is more flexible and convenient.
The number of bits that would be required to detect the registers would increase with more registers, this results in the lowering of the number of operations.
When a program would involve CALL subroutines the status of the registers would have to be saved and restored often, this would result in a significant overhead for the processor.
Higher the number of these registers mores space would be used by them on the chip. This can create problems in adding / implementing other functions on the chip.