Even if we wipe ourselves out tomorrow, that still means that a civilization was able to broadcast its existence for about 80 years. If the Great Filter is now or ahead of us, that at least implies that pre-filter civilizations can be advanced enough to signal their existence.

At some point our signals will be too weak for anyone to pick up or distinguish from cosmic background noise, which probably limits the radius of the sphere of stars that can hear us, but anyone inside that sphere gets at least 80 years to be listening to potentially hear us.

So, even if civilizations only last for say 100 years on average, and you can only hear other civilizations within N light years, if N is big enough eventually someone should hear someone, and if N is really big enough, somewhere in that 100 years everyone should hear at least one other someone.