Comment by rustyhancock

Good question, I think it's to get people drunk and buying more drinks.

As opposed to the crowd sobering up and leaving.

But also I believe the bar (staff) often genuinely don't know what their serving is harmful.

I should have added the limit to safety at low levels of methanol is actually that your body processes ethanol much faster than methanol. So it's more that the crowd goes home and then hours later (once ethanol has been cleared) the methanol finally is picked up by the enzymes that makes it toxic. If they stay drunk (on ethanol) for days the methanol might have been excreted before being toxified.