A rung on the gearing ladder
The raid finder, when it first appeared, was famously exploited for gear by guilds -- and indeed, it still is, although within the rules. Gone are the days of the glitches exploited by Paragon, landing themselves a ban. But those issues aside, the raid finder has become very much a step on the gearing ladder for any new character, and guilds put this to good use when gearing up their colleagues, going into the raid finder as a group or with several people all on the same token. So if a guild member had a new priest to gear up, a guild might join as a party of paladins, priests and warlocks to get that new priest several rolls on token drops, as the tokens could be passed between players.
Offering as it does not only higher item level gear than heroic dungeons but also tier pieces and the associated set bonuses, the raid finder was a valuable source of easily obtained upgrades for a new character. And so as it progressed, more and more players came into it that were cheating the item level requirements, making the fights longer and the rage more ragey. Do you remember the start of the raid finder? When the instances were new? How polite and excited people were to see the new boss mechanics! It was actually fun then.