The lease previously negotiated by the past regime has little relevance as Twitter is currently occupying less than 50% of the floor space.
The landlord has to either accept lower payment, or look for a new tenant and Twitter moves to Austin. Given the current environment in SF, it's likely a new tenant won't be found for years.
Landlords have to take a hard line. They negotiate with a tenant and then the whole building stops paying rent the next week.
The same thing is happening in retail as offices. Rents are, mostly, way higher than the market and landlords are quite happy for that to continue. Eventually the market is going to crack, I think everyone has acknowledged that...but landlords aren't going to be the ones to crack it themselves.
Sure you have a contract but you need to enforce it. So you have to sue which takes time - a lot of time.
Then you “win” but the other party can still not pay, or they could appeal - back to court and even more time.
The landlord has an iron clad contract sure - but Twitter has what they want ($) and the leverage as a result.
Note the landlord here is a big national firm. They're not going to be scared off by having to take things to court, and even beyond the $ at stake, they're pretty highly incentivized not to let customers wriggle out of paying leases just because there'd be lawyers involved in enforcement.
That being said, I would bet the article is just lazy journalists trolling for clicks as usual.
It likely is true that the landlord can legally force Twitter to pay up, but if that leads to Twitter’s bankruptcy, they won’t get the money.
Also, if they end up with a building that isn’t rented out, they may have to devalue their property and take a huge administrative loss. If their personnel’s bonuses are somewhat tied to their balance capital and/or revenues, their employees won’t want to end up there.
It is a bit of playing chicken. If the landlord thinks Twitter will go down if they play it as hard as possible, they will (grudgingly) accept changes to the lease contract. A common tactic is to decrease rents per m² or decrease the amount of floor space in exchange for restarting the lease period (e.g. if they’re in year 4 of a five year lease period, halve the rent, but start a new five year period). That way, the landlord can (somewhat) declare this as a victory because there’s more ‘certainty’ that the property will still make money in three years time.