By lowering brain temperature and maintaining thermal homeostasis, the thermoregulatory theory suggests that instead of prompting sleep, yawning actually serves to maintain focus and attention, thereby antagonizing sleep.
So not concrete but it is one of the prevailing theories for one of the reasons we yawn
A quick Google does not name this as one of the several reasons for yawning. Any sources on this?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3534187/#:~:text=By lowering brain temperature and,and attention%2C thereby antagonizing sleep.
So not concrete but it is one of the prevailing theories for one of the reasons we yawn