Why does the boolean modifier function so poorly?

Is there a reason the boolean is so terrible in blender? I’ve been trying to boolean this tree for 3d printing for 3 days now. I have to move the piece a little, doesn’t work, move again, doesn’t work. Over and over for hours and maybe get 2 pieces join. It seems to be a terrible modifier. I’m even using a boolean add-on and it doesn’t like joining these together. is there any sure fire way to get this to work more often? Here is my file https://www.dropbox.com/s/mq66ehb7qyb4zk9/2x2%20Forest%20Wall%20A.blend?dl=0

It seems like you’re trying to boolean non-solid objects, which is making it unnecessarily hard for Blender to identify the structure of the mesh. Booleans usually work best with solids in Blender.

Look at the messy mesh inside your object. You need to clean this up.

If you want to 3d print you don’t want internal meshes

I’ve even made them solid and still doesn’t work.Making them solid didn’t change anything at all in the last 3 days.

Could you try Blender from buildbot (not the experimental), and see if boolean modifier works better?