Since it is conventional for English-language anime-listing sites (e.g. MAL) to treat a break in airing as marking the end of one series and the start of another, you need some way to differentiate between the series that ended before the break and the one that started after.
In the case of something like Naruto, the second part had a different title ("Shippuuden"), which makes the task of naming the new season easy (i.e. just call it what it is). Since Fairy Tail was called "Fairy Tail" both before and after the break in airing, you need some way to distinguish between the two series on the anime-listing sites. Using the year in which the series started airing is as good a way as any.
I should emphasize that this is purely an artefact of the way that sites like MAL name series. As far as the people producing Fairy Tail are concerned, the episodes that started airing this month are part of the same series as the episodes that aired from 2009-2013. If, for example, you consult the timetable for TV Tokyo, which airs Fairy Tail, you will see that this week's episode is listed as:
ＦＡＩＲＹ ＴＡＩＬ ～フェアリーテイル～「妖精軍師」
This is the same title that was used for the show before the break in airing (the last bit is the episode title "Yousei Gunshi", something like "Fairy Tactician").