How do you know there are 45 seats left on the plane? Seat maps show how many seats are unassigned, but say nothing about ticketed passengers who don't have assigned seats yet. You can't add seat availability in all the fare classes because those are the same seats, just available at different fares with different terms and conditions. (Also, EF and other consumer booking engines never show more than 7 seats available, for technical reasons involving multi-user access to the underlying database.)
In any case, fares tend to go up in the two or so weeks before a flight because people who fly on such short notice typically don't have much choice. They have to fly at almost any price. Those who plan further ahead generally have more options, so airlines have to offer lower fares to get them.