There are four different verses about banning wine. Islam firstly said do not pray while you are drunk. And step by step made harder rule. Then, finally said wine is Haraam.
Why not in just one step?
When Qur'an was being revealed to Arabs, it was being revealed in stages and it was something new for them and it was supposed to be implemented in their lives and not just recite it. So, these changes were brought gradually and not suddenly, and this is a mercy of Allah so that people could adjust to these new prescriptions.
The verses in Qur'an about drinking wine is an example of that. Wine drinking was very common in the pre-islamic Arabia and although, it was evil, it was considered with high esteem. So, there were three verses which gradually lead to prohibition of intoxicating substances. It was revealed in stages - Qur'an 4:43, Qur'an 2: 219, Qur'an 5:93-94.