Why are only 5 bits of the IRQ id used for irq_id_o and exc_cause_o?

Created by: Silabs-ArjanB

I see in https://github.com/openhwgroup/cv32e40p/blob/master/rtl/riscv_controller.sv that only the least significant 5 bits of the IRQ identifier are used when assigning irq_id_o and exc_cause_o. Furthermore irq_ack_o is only asserted when irq_id_ctrl_i[5] and not for the other interrupts.

Could you explain why not all interrupt sources are being treated equally?