Because change is going to happen whether you want it to or not.
If you're status quo is gaining weight -- you need to change your behaviors -- behaviors are what got you to the weight you are. Or, if your not going to not change your behaviors --your weight will be what keeps changing.
I'm shocked at how many people just don't understand the change principle. You can fight it if you want. Argue with it. Not like it. Complain about it. Whatever. Change doesn't need your input -- it's rolling already.
You, however, may want to put your own spin on change. Maybe you want to change direction. Maybe you want to control the speed. Those options are open to you (sometimes, at least).
I'm sorry you don't like it. (and I honestly, mean it! I don't always like change either) But whether I like it or not has very little bearing on what needs to be done. You're not going to be able to reason or argue you way out of change. AND you're wasting precious time and energy when you try to.... (who has so much energy that they can waste it?? --not me or pretty much anyone I have ever met!)
So pick a direction. Decide what change you can deal with, pick up that ball, and move it along. (You don't really have a choice).