I got my "law degree" from watching TV, so take this with a grain of salt, but when you apologize you are admitting fault, which could be legally binding if a lawsuit is brought upon you.

So if he were to apologize, Red Cross could then potentially sue over a down tick in donations due to the join campaign, etc.

Again, not a lawyer, have no real interest in law, but this has played out on TV shows a few times.