Again, you don't advertise something without it having good potential sales in the first place.
You don't spend millions in marketing without it paying dividends first and you see a trend.
Really simple example MCU films barely had big marketing pushes. Then they got popular, now they have huge marketing pushes.
I'm also not sure what you are trying to say here. People buy manga because they like said manga lmao. A marketing push isn't going to get people to like shit and consistently make One Piece sell 500+ thousand copies over the #2 or sell 1+ million every release. If it was objectively bad to Japan, it wouldn't sell. End of story.