They're not really concerts, they're events and, as such, draw in vast quantities of people who wouldn't regularly attend music performances not in stadiums. They shouldn't be thought of in the same pricing category as regular concerts. Hence, super high demand and people prepared to pay a premium to be able to make duck-faced poses on their Insta with a band playing in the background, all living their best lives, singing the wrong words to Live Forever with their bezzies, you almost literally can't put a price on it.
Anyone truly interested in the songs would have gone to see Liam play them in much smaller venues a few weeks ago. This is for people to check an empty box in their lives which says "I have seen Oasis!" They don't actually care about seeing Oasis, really, they just want to be able to say they have had the experience. I don't begrudge any band/brand exploiting their market worth in these circumstances.
Besides, since almost everyone here says they can't stand Oasis, why the kerfuffle?