I used to think I was okay at making plans, until I met people who are good at making plans, which led me to conclude that I am, in fact, bad at making plans.
An important difference I've noticed is in how we build plans on top of one another. If a friend knows you are working until 3pm, they might suggest having coffee at 3:30pm. This is really one plan (coffee at 3:30) stacked on another (work until 3). Intricate as it sounds, this is well within the remit of an okay planner. What good planners do isn't just make plans, but support the ways that others stack plans on top of theirs.
One part of this is providing good plan-building information. Things like if you finish work early that day, or you're working from a different location, or you have an appointment at 4:30. Even if none of these things make a difference to you, they might affect your friend's preferences. Maybe, if they knew, they would suggest an earlier time, a different day, or meeting closer to your appointment.
Another part is being aware of what information others might use to plan. Perhaps you once mentioned you like pickles, but you've since gone off them. Could your friend have made plans to go to a pickle cafe? Or perhaps you mentioned that this week has been very busy. Will your friend assume it's a bad week to get coffee when actually you would welcome the break?
And another still is structuring your plans in a way that is easy to plan around. Maybe your finish time is flexible, but 3pm is what you tell people in case they want to spend time with you.
All of these things require what is, at least to me, a higher-level skill. Not planning, but having an inherent sense of how other people are planning around you. Providing others with the information they need to make good plans actually means you need to do less planning to achieve the same outcome. This can make the process seem deceptively easy to an okay planner.