We’re designed not to expend energy, as for most of the human race’s existence, food was hard to come by.
Early humans didn’t go for a jog for fun, there were no gyms, we got food and then rested.
The other thing, doing things that were potentials for being ridiculed and ostracised from the ‘tribe’, so for example things that had a risk, stopped us. After all being shut out had serious survival consequences.
So we have to override these mechanisms that stop us from doing stuff by making it simple and easy to do.
Start small, take little daily steps and make it simple.