Sure, let me explain it to you.

The end result is not recreatable with digital assets. i.e.: It doesn't matter your budget, we cannot currently simulate the look of the original footage shot on 35 (let alone 70mm, forget about IMAX 80mm) by shooting digitally.

Also what you're referring to as 'garbage', is colour grading and composite work. It's not adulteration, it's an essential create part of the filmmaking work. Whether you're doing it exclusively as part of the development process of the physical film, or digitally in Nuke or Resolve etc.

Your inability to understand why people do things in a domain you're not familiar with is indicative of gaps in your knowledge, not the futility of the process. Lots of information about how and why all this works as it does online.