Why don't these /execute parameters check for the entity in the specified position?
Your command is testing for an entity with the selector @e, which is any entity. This will almost always be true while you are on the world / server.
The positioned means that the command is ran from the location, so if you did /execute positioned x y z run setblock ^ ^ ^ stone then the block at x y z would be set to stone.
The correct version of this command would be:
/execute positioned x y z if entity @e[distance=..1] run fill xyz1 xyz2 block
And obviously you would replace x y z, xyz1, xyz2 and block with your own data.