Vaan did not have any special intent in creating an ancient ruin; he just thought he could make the scenery look less plain and boring while experimenting with the power of thought.
Moreover, creating the ancient ruin, moon, and stars required low effort.
Thus, it was easy to do.
If he wanted to make a much more complex scenery, like a human city down to the minute detail, it would quickly consume all his soul power, and even then, he might still fail to complete a part of it.
After all, the power of thought consumed soul power.
But more importantly, even though the power of thought was easy to understand, executing it was not as simple, and could even be extremely difficult for many people to master.
It wasn't something that could be changed with hard work; it required talent to understand, and even more talent to master.
In simple words: You either know it, or you don't—Just like maths.
