At some level even if you know basic moves those moves are wrong.
Some things are hard to express in code even if you know exactly what you need to achieve and you know all the basic moves like loops and if statements.
If you know that you have to do a check mate or get amount of points and you know how to do basic moves but you don’t know any openings you are going to loose in 3-5 moves. If you get past openings you might get to 15 moves. If you do easiest greedy approach you loose if you take easiest defensive approach you loose.
It is not „what to program” because in chess you exactly know what is the goal. Getting to that goal alone is hard.
Like what? Are you, perhaps, confusing "hard" with "time consuming"? Some things take a long time to express in code (absent AI, at least). It's not hard, though. It's just rote copying down what you have already determined "what needs to be programmed". Getting to the point where it is just rote copying can be difficult, but is decidedly in the "what to program" phase.
Giving an example will take too much time from my perspective in regards to how much time I am willing to spend here arguing. Have a great day