People aren't paying for the lifestyle of multi-millionaires (or, in this case, their massive alimony payments). Indirectly, yes, that's a consequence, but what they are paying for is the chance to see a band they love live, do something they will remember for ever. It's not my choice, I don't dislike Oasis but I am not a fan to the extent I would want to go to a gig, but I get why those who are want to go.
Most of the people complaining about the COL on here seems to be middle class parents telling us all they are barely surviving on £100k a year and crying about how they haven't had a holiday in 3 years. I don't see you posting about how there can be a COL when people are still sending their children to private school, eating out or spending money going to see a West End show, but plenty are still doing that.
I think this has to do with a perception about Oasis fans. I've got a feeling you imagine the 14 million are all either living on benefits or low income. They MUST be paying for this on a credit card, how else could the paupers who like this sort of thing afford it? I can only imagine that's it, since you haven't expressed any issue with people spending money on, say, tickets for the Olympics in Paris, which will also have attracted millions of people wanting to go and will have also cost a fair bit.
As someone else has pointed out, Oasis have a worldwide fan base. A good percentage of the 14 million will be coming from overseas. Those from the UK will likely have been in their teens/early 20s back when Oasis first burst on the scene and might now live in a nice 3 bed semi with a low/no mortgage, but even if they weren't, what they spend and how they managed to do it isn't your business.
I'm not sure how many dates they are doing, but I would say a good number won't be spending a thing as they will not manage to get tickets. You can then cheer because they will have been saved from themselves.