Try to set up an embassy there, see what happens.
East Jerusalem always was the “de facto” capital of whatever passes for Palestine, more a mishmash of various tribal affiliations than in any way a nation-state.
Nothing has PREVENTED the “Palestinians” from declaring themselves to be a nation, other than their own internecine conflicts and petty jealousies between factions, and an unwillingness to come to some concrete proposals other than “drive the Jews into the sea”.