That's not how "cause of death" works. Doctors/Coroners don't just pick a cause randomly they look at how you died and actually investigate it if it can't be readily determined.
Presumably you think doctors have always been lying about cause of death? What do you think their motivation for that is?
I don't think this is what they're saying. I think the point is that those people's actual times of death weren't far enough from their expected times of death given their preexisting conditions to be able to confidently say that they died of Covid, rather than just having died with it. In other words, that there's a good chance they would have died at the exact same time even without Covid.