Well because I actually know the science behind it and know what the body prefers... also, in terms of cardio vs HIIT - for fat loss one is best, for cardio fitness one is better. It really is that simple.
As for the keto diet, you've just admitted yourself it comes back quickly if you don't change your eating habits. How about, just changing your lifestyle, so you don't have to worry about macros and eating specific items, and just eat well all the time? It so much easier.
Without wanting to sound arrogant, and I know it already does, I do have a bit of a clue as to what I'm doing. I never claimed it's rubbish, I claimed that as a lifestyle it is untenable and just not necessary. It works, it's plain biology, however, the effort put into it could be used to just life a healthier lifestyle from the outset.

I feel the same way about IF. It's just another way of calorie management, nothing more.
Go with whatever works for you - for me, it's too much of a faff.

There is no right or wrong way - however, to be honest, lifestyle change is more important than diet - there's more to lifestyle than just food intake