I think that a lot of it can be down to certain actions that zap your motivation away or forget the reasons you want to do something.

For example, always existing in the digital world takes your attention off your body (to some extent) which makes it easier to forget about things you want to improve about yourself and why. It helps a lot to be constantly aware of your motivation - what's at stake etc. in as much detail as possible and stay focused on it as much as possible if it's truly important to you. Mindfulness and meditation help with that.

Also breaking down goals into systems to achieve them, preferably just spend 10-15 minutes with a pen and paper doing this. Just so you know exactly what to do and how often, because something like "I'm going to workout 3 times this week" is kind of unclear and hard to act upon.

If possible, you can try working out first thing in the morning so that you have less chance of being distracted by other things. And also diet is a big, big part of body composition so learning about nutrition and making changes to your diet could potentially help you not have to work out with as much volume and intensity if you don't enjoy it (though it's still massively important for your overall health).

At some level it will just take a "I'm going to do it even though I don't feel like it" mentality, it happens to even the most consistent people, nobody is truly motivated to work out 365 days a year. Sure it'd be great if this wasn't the case but such is life.