My trainer and doctor say that we have various receptors in our bodies tuned for our current way of life and that diet and exercise re-program these receptors which, yeah, is what I observed as well.
RE: your lack of motivation for working out, I found it is related to the type of exercise. The start of my journey was a series of train wrecks. I constantly stumbled on 22-year old boys whose wisdom was "get on the bench press, bro!" which didn't work for me. It was almost harmful even.
After going to physiotherapy for a while I then started training under the tutelage of the same people and I am already better. They are very careful not to over-strain me, give me just enough cardio to keep my heart pumping but not to make me wanna die, exercises are carefully tuned to strain me a bit but never too much. They don't give me big pauses between exercises (60 - 90 seconds) however. Some exercises are mostly stretching and "activating" a certain muscle (meaning just exercising it a little without any strain).
Not sure I can translate that to a workout strategy for you but these items might help:
- Do 3 series of each exercise. If it's too much then 2;
- Do more reps per series;
- Rest until your heart calms down slightly but not beyond that;
- Introduce a hard cap on the workout session -- mine is 1 hour. This was a huge struggle because I wanted to do all the exercises but there's no way to fit all in 1 hour (did that mistake several times);
- Start with slight cardio -- 5 or 10 minutes. Don't make it the focus of the session, it's just to start you off (a mistake I made many times);
- The moment you start feeling a tormenting strain is the moment where you train for 2-3 more minutes and cut the session short;
- If that moment doesn't come, still stop at your time cap.
The main point is to feel energetic and rejuvenated after the workout. Not "OMFG I wanna die!". My trainer / physiotherapist / masseur told me this is an extremely common problem for men because a lot of them just hang out in the gym and their main motivation is show-off and competition with others. He says there's a million ways to make yourself feel better by exercising and honestly? I believe him because it is happening to me.
Finally, it's the most normal thing in the world to fine-tune the exercise session to your specifics and you shouldn't try and imitate other workout regimes if they don't work well for you. My trainer quickly found out I have strong arms, shoulders and upper back and is rarely giving me exercises for them -- just for maintaining them a bit. But my legs, abs and lower back are weaker so 80% of my exercises focus on that. Works great.
If you are willing to press on, I wish you good luck. I am exactly like you, I view physical maintenance as nuisance and it's not easy to change the mindset. But I already started having that little little voice in my head that's sometimes nudging me to do a session because I know it makes me feel a bit better after.
In programming terms, I'd say reduce the size of the program/tests until it's manageable for you. My trainer said it's much better to train every day for just 35-40 minutes compared to two workouts of our and half a week.