The only reason this seems like an unusual definition to you is that you haven't thought about it very hard, yet. The critical thing is not how many XMR you have. It's what value those XMR carry. If I create from thin air 1000 XMR and it's known to the market I didn't just 'make' a certain amount of value, I made myself richer by making a lot of people less so. I stole value from them and gave it to myself, just like someone stealing a ham at the market. The only difference is that instead of burning one ham of value for one ham of benefit, I burn many ham of value for one ham of benefit.

This is an excellent explanation and I'd also point out that it generalizes to fiat not just crypto. But its nice not to think about that too much.