Why do Maroon 5 keep advertising sold out concert?

This morning on Twitter I posted a screenshot from today’s Bangkok Post. Yet again there was a large colour advert for the sold out Maroon 5 concert. I asked my followers why they thought they kept doing this. I suggested that if they had a surplas advertising budget that maybe they could donate this advertising space to a charity. Here are some of the replies that I got:

• RT @dacheah: Good idea! Takeaway outlets donate unused food 2 charities daily. Why not the same for media ads?
• RT @Vexape: Would be great. But sadly big business rarely helps charity (as much as it should).
• RT @Calzo: Reason is that they have already paid for the advertising so might as well plug their new album as long as they can.
• RT @nilvachararang: Not only maroon5 are in the ads but their sponsors. To keep the public awareness, I guess.
• RT @laragirl78: They can’t. Media planning and buying is already set and paid for.
• RT @randyhate: Most likely in contract for ad spending. would be GRAND if artists would allow for charity after sellout though
• RT @Calzo: A promoter for a large record label will purchase a block of advertising right up until the show before any tickets sold.