A) is perfect idiomatic English and means what you think it does. His course of action is to stay open, the pandemic was a negative in that decision, but not negative enough.
The idiom is a negated negative-sounding word (examples below) followed by "because of". Whatever comes next is a reason against, but not strong enough. I did a search for some examples using: [don't "because of a"]. You can see they follow the pattern:
"Don't miss out because of a first impression", "Don't ruin a good today because of a bad yesterday", "Don't punish all who need help because of a few who cheat", "Don't turn away business because of a pet!", "Don't quit because of a vindictive person". I also found "I'm not going to lose him because of money". Losing is bad, not losing is a double-negative, so it's understood to be a lack of money, not that they will use their vast wealth to keep him.
Over to B). That's not as good since it's nothing special. They avoided using the well-understood "because of". Maybe they avoided it since that's not what they meant to say. So now we have to decide whether the pandemic was a a positive tipping factor, or a not-good-enough reason against.
For a contrasting examples, suppose some music started playing, after which we decided to stay where where we are. "I'll stay because of the music" is easy -- it's the reason we're staying. "I won't leave because of the music" means we're staying in spite of it. "I won't leave because that music is playing" is less clear and probably only makes sense in a larger context.