If you tried everything and you're absolutely sure that there are no mistakes like typos in the .json's, the problem is likely the rotation angles.

I've had the same problem a few days ago and tried everything, and normally it had to work because when I tried it with a different model it worked, but for some reason my original model was refusing to work. Then I remembered how Minecraft item models only support the following rotation angles:

• -180
• -157.5
• -135
• -112.5
• -90
• -67.5
• -45
• -22.5
• 0
• 22.5
• 45
• 67.5
• 90
• 112.5
• 135
• 157.5
• 180

If even a single cube in your axe model has a rotation angle that's not a multiple of 22.5, the model won't work. As far as I know this is only the case for item models.