They fail because they're unsustainable. You're trying to replace habits with rules, habits will win out.

Make new healthy habits. Nothing too extreme, a little at a time.

Cut soda. You'll be surprized how much weight you can lose with that alone. Drink water instead, or other sugarless drinks. It sucks at first, but after a few weeks, you get used to it, and a few more weeks after that its not even a thought.

Remove other unhealthy things, one at a time, slowly. Make them habits.

Slowly introduce positive habits; go for a walk, 30 minutes a day. Its not hard, but it can feel shitty at first. Just push yourself and soon it will be your routine, and eventually it'll be a habit that feels wierd to break.

Small change over time are the key. Trying to change aubrupty doesn't work because your brain seeks those things out even harder when you try an tell it no.