Because Lincoln refused to discuss the matter at all. You blame them because *HE* refused to engage in "discussions"? They sent authorized agents to discuss the matter back in January of 1861, but Lincoln refused to meet with them.
It also wasn't federal property after the state seceded. It escheated back to the state.
Also, the violence was started by Lincoln who sent a fleet of warships to Charleston with orders to attack them if they did not cooperate.
It was the arrival of warships that triggered the bombardment of Sumter. There were no plans to attack Sumter until the warships were sent.
If you did not know about the warships, it is because you have been taught history which deliberately omits this bit of information.
You've been taught deliberately biased history.
I remember reading the many speeches in Congress about the issue and of course there would have been endless informal meetings to find some resolution to the impasse.
Davis talking informally as one Kentuckian to another was the only hope of avoiding war.
When Anderson initially left the other forts around Charleston harbor, he told folks in Washington he did not need to be resupplied. Afterwards he revised the statement to ask for help. The ships that came were not a warship convoy, but those needed to resupply him. Davis could have decided there was no reason not to allow him to be resupplied.
The forts were federal property and would not automatically revert to a state, but their fate would have been decided as part of secession negotiations. Mary Chestnuts Diary makes clear Anderson was given an ultimatum to surrender and bombardment began after the deadline passed, and not because Union warships were or were not present. I’ll stick with my understanding of history.