It might be hard to understand if you're an M+er or a raider, but the outdoor content takes a while to gear up in if you don't do those things, and it caps out at a level that leaves a lot of the content difficult to do on one's own. Catch up gear lets those players get stronger in the content they want to do by doing the content they want to do - as it should be for every aspect of the game - and makes it easier for them to do the content without having to rely on other people happening to be in the zone (hunts, rares, the siege, etc).