Actually, i am thinking that this could be due to limitation of the software and then OS limitation as well.
Try to create a raid 5 volume less than 2TB, and let me know if there is any difference.
If yes, this is the reason. As far as i know, i never come across Bootable No after creating a new raid volume. I did see it when i had a failed raid array.
I have attached a screenshot as a reference for you.
All the best,