Why this sentence was not accepted? "Sok turista a repülőtereken van."
It sounds a bit strange and has a clumsy looking but it's all right. Third possibility:
" Sok turista van a repülőtéreken".
You put the airports in focus, while the sentence above puts the tourists in focus. Whatever is in front of the verb is emphasized. So, your version is somewhat unusual, but could be useful in some situations.