I can't speak for NYC, but in Sydney commercial properties are typically valued at a fixed multiple of the rent. This matters because if they change the rent,

I can't speak for NYC, but in Sydney commercial properties are typically valued at a fixed multiple of the rent. This matters because if they change the rent, any loan they've taken out now gets revalued, which could put them underwater. So in that case 80% is much worse than empty but at 100%. This is why you'll see landlords giving a month's free rent, making rebates etc, while technically still charging 'full price'.