The rules are very simple:
Each member of the local board (except legendary members) can submit merit-worthy posts once per month. They post the links and the number of merits they feel their posts deserve. qwk then checks the submitted posts, and rewards merits according to his subjective opinion. That can be more, but it can also be less than what the individual members think.
He doesn't send those merits every day, and usually does it a few times per month. That's why you see a long list of merits awarded to bullrun2020bro on December 17. But not only to him, but several other users such as SiNeReiNZzz, Koal-84, seek3r, Soonandwaite, etc.
You can check qwk's merit history here https://bitcointalk.org/index.php?action=merit;u=24140. Check and you will see that each given merit points to a post that was posted by that user in qwk' merit thread.
I can in good conscience stand behind every single merit I awarded to bullrun2020bro.