Because Arenanet seems to have not erased MMR, league play is just one giant grind to get to a legend rank that means nothing.
As long as the game still makes matches based off MMR and not league rank, you could have people with 1000 mmr in diamond tier vs other 1000s, and people with 3000 vs other 3000s. It doesn’t make any sense, but it looks like leagues will be another failure in an extremely, disturbingly long line of failures for PvP infrastructure.
On a brighter note, the Guild Challenger league IS MMR based and I think will be healthy for the competitive scene.