No one's forgetting it, it's just intangible fugazi.
No one knows how much Messi brings in to the club, but most of the money he "brings in" according to the report made by a presidential candidate looking for Messi's approval is in long term sponsorship value.
They don't actually lose money if he goes, they lose it in 1/2/3 years when the sponsorships are renegotiated.
A contract like that is very likely to have a "Messi clause" whereby if he leaves the club, the payments go down.
They will lose money if he goes, so they will definitely make him the very best offer they can. It would be a false economy to let him go.