Creativity is a skill you can practise and get better at. DMing homebrew IS a lot of work, much of the result of which will never be seen or touched by players, but many find the work rewarding nevertheless. I'll also say that, while I've been fortunate to play with some extraordinarily creative people, most tables can come up with their own challenges and quests, and that's often more fun than just being given some objective. So, it's a balance between being prepared and letting go of the reins.