Premium to fly from Brussels airport

Airline pricing is very much based on ‘what the market will bear’. Typically, on any flight, a quota of seats at the very lowest fare will be offered, then a higher fare, then a still higher one and so on. These quotas are generated by extremely complex computer programs, the process is called ‘yield management’.

Since the journeys you mention consist of either an Amsterdam-Madrid or a Brussels-Madrid, joining onto a Madrid-Canaries leg, the price will be determined by the market situation of the Brussels/Amsterdam-Madrid sectors. It is very possible that on the days in question all the cheap seats on Brussels-Madrid have already gone, while there are still some left on Amsterdam-Madrid. It could well be that Brussels-Madrid is more of a business route, to the quota of cheap seats is smaller in the first place.