New Year's resolutions, despite being often criticized as a fad due to common abandonment, can indeed serve as effective tools for self-improvement when formulated realistically, tracked regularly, and approached with a resilient mindset, turning them into tangible steps towards one's personal growth.
I think its just a FAD from gym & fitness industry to get a years worth of subscription fees. Just makes you to postpone something tomorrow what you should start doing today. New year is just as good as new week or new month or birthday or anniversary :).
Having said that, unfortunately, I fall for it every time :(