Short answer, ghost rating thinks you should be playing the top teams. Grats!



Long answer, we are facing a stagnation of the arena system due to a lack of available item upgrades at the lower brackets, resulting in a decline in the number of teams playing. This is easily shown with some math: per Blizzard, the definition of a 1650 team in both the new and old system is “Better than 68% of all teams on this BG in this bracket”. Given the lack of items below 1650, the majority of players who play arenas for 4 to 6 weeks will have as many arena points as they need to buy items.
Furthermore, pnce you've bought the gear available, the reason to play other than "I like arenas!" or to do 10 matches per week to stockpile points, would be to try and move up rankings to unlock new gear. However, most people will rather quickly become skill bracketed by the match-making rating and find it difficult to move up beyond what their skill dictates once they've obtained bracket-appropriate gear.


Hard numbers :

If you are below 1615 rating you need just 1475 arena points to buy every arena point item that is available to you. Since teams below 1500 are awarded points as if they are a 1500 ranked team, it takes 5-6 weeks max to earn this many points at any rating below 1615.

If you are 1650 rating max you need 2075 arena points to buy the 5 piece armor set (hateful legs/gloves, savage helm/chest/shoulders). This will again take 4-6 weeks to earn the points depending on what bracket you are in.

If you are 1775 to 1850 player, to buy a full set of Hateful takes 3050 arena points. This takes (again) 4-6 weeks at most depending on your bracket.

Above 1850+ there are some more expensive items, and above 2K you have weapons/ranged unlocked. So you need more weeks of playing to get those points. But only a tiny fraction of players are 2K or higher. And the more people that stop playing at the low brackets, the fewer high ranked people.


Also, the 350K+ honor points needed to buy a full set of PVP gear is not an insignificant time investment, pushing people to BG's instead of Arenas. On top of this the availability of alternate main slot PvP gear outside Arenas (Vault drops, WG tokens, badge gear) means that in actuality players need even fewer weeks of arena matches to earn their points.