Problem is that they're offering a 4 year contract on £400k a week, even if we match the length of the contract, £130k a week would mean he's giving up almost £60m over the next four years.
In your scenario I'd absolutely stay at United making £4m less, but would I throw away the chance of making an extra £60m over for years? If everyone is being honest with themselves they'd take the money - and there is no shame at all in that.
More importantly, Ighalo has been a breathe of fresh air, and it highlighted what type of character we want to see at this club - hopefully he does the crazy thing and signs here long term.