Cynical answer - the current laws don't allow it; they won't change to accommodate what is actually happening; football clubs rely on police approval and police/authorities wouldn't fear controlling a football ground and who should be there.
Hopeful answer - by the time the play-off final comes around if cases continue to fall, and if there are no spikes from protest crowds/people going shopping/leisure etc then government might reduce lockdown further and we get to go the final.