I suspected you were wanting to use SimC weights.
Read the links about stat weights, even the guy running Raidbots has a disclaimer about how they’re bad and links to a few different discussions on them, one of which I provided earlier.
If you’re just reading a guide and using the weights they provide they’ll be from a fight against a target dummy with zero movement and using the best gear.
That isn’t a useful place to start as the gear you have to get you to that point is not the same, also you don’t have the option to just stand still and cast ignoring all mechanics.
You can sim the gear you’ve got vs the BiB result vs what other sources are telling you and see the difference, it’s probably close enough that it won’t really matter.
If you’re unsure how to run those sims paste your addon export as a reply and we can see what you’re looking at and set the sims up for you.
Occasionally BiB gives me unexpected results so I run some sims to see, it also chooses a trait I’m not fond of so I’ve used the customisation option to give me the best, from what I’ve got available, without the traits I don’t want to use.
In my case that’s Undulating Tides & Iron Jaws, while they’ll do more damage - in an ideal situation like a sim fighting a target dummy - in a real fight the uptime on Undulating Tides is not worth it for the fights I’m progressing on. Iron Jaws is only slightly better than the second trait and isn’t useful in M+ and rather than reforge for content I choose the tiny decrease in potential, if all the stars aline, single target damage.