Dual boot for ROG

I have set up dual boot on my desktop before. My question is for the hardware.

Both motherboards are ASUS but why can only one have a capability from the bios to select the boot order?

I had upgraded the bios in my Asus z170 motherboard in my desktop, and that is also the motherboard that I had used to dual boot. But with my ASUS ROG GL502VT laptop there is no boot order selection, i am willing to update the Bios if that is what is needed.

Hit escape on the ROG splash screen.

https://rog.asus.com/forum/showthread.php?10016-Help-Booting-from-cd-with-Asus-g73jh