Well, out there you can find thousands of articles telling you that booking in advance is something that will always help you get cheapest flights. Completely agree. What I really would see no point in doing is to write another article telling you the same.
Instead, I just wanted to write some quick notes for the curious ones on why this is a strategy that airlines use? Why do they benefit from this?
There are a few reasons that make it happen. To understand this, we need to figure out what will happen if this strategy was not in place. Of course, we humans love to do things at the very last moment, and a massive amount of people will get to book the flight on the last day. Why to book earlier? Imagine that for some reason you need to cancel it! Of course, we are not stupid, and we would do it the very last thing before departure.
You could tell me that some people would book earlier for the fear of running out of places. Could be, but if we take a look at the planes nowadays, you will realize that there is always some places left except in the major holiday dates. That would be another article, but here it comes one of the main reasons why extra-discounted tickets exist!
Why airlines are not interested in bookings happening at the last minute? Well, they need to plan in advance for many reasons. Knowing the occupancy of the planes will let them analyze the situation and vary the prices accordingly, they need to plan for the food that they will need for this flight, and also for the space required for baggage. If they knew an airplane is going to be nearly empty they are on time to make changes and select a smaller airplane to do the trip.
At same time, the people that normally book at the very last moment are the ones traveling for business reasons. As discussed in other article, business travelers are expected to pay more as their companies are the ones who pay the airfare, so the fares are planned according to their needs. What I mean is that a high fare will not scare any company, but it could scare lots of tourists. Better let tourists book before as they have reduced budget, and then the business travelers will have no problem in affording higher prices.
Short and easy. These are the reasons for airlines to have better prices for the first seats occupied.