That is really dumb logic. We should have elections every year then. Actually every day, because many old people die daily and young are born too.
1. referendums aren't elections.
2. I explained the reasons why an election shouldn't be done every year in my following post.
3. results of general elections have an impact within a few weeks after the election is over. This referendum will start having an (legal) impact almost 3 years later.
Question: Would you make a final decision 3 years in advance for something important and then stand with it no matter what things have changed in the mean time or would you rather check if it's still the right decision some time before the deadline ends to make the decision?