That we are, apparently, if we don't understand why slapping a hub world somewhere without tying it to any actual plot or theme whatsoever and thinking it's going to produce cares and feels is a bad idea.
As someone else wrote...
It's the center of the galactic economy, has the largest economy of any planet, is the homeworld of the most powerful race, and has one of the largest, if not the largest, stockpiles of eezo in the galaxy.
Thessia is completely justifiable as being a center of operations for the galactic resistance. There's your plot reason for Thessia being a hub world. The war effort that Shepard is involved with is organized around the world.
Bioware wants us to care about the world? Make us. Through interactions in that hub the player could be shown how the world is key to the conventional war effort against the Reapers. You see how it is a hub for supplies, transporting troops, taking in refugees, repairing and refueling warships, etc.
As the defenses fail (there should be an emphasis on the Asari and their allies deploying massive military might in defense of the world) and the Reapers overrun Thessia, it's more than just another planet. Not only does the player now have exposure to the characters and location being smashed by the Reapers, they see the backbone of conventional military resistance being broken. They are being forced to retreat from their homebase.
With the Reapers seemingly delivering a crushing blow, we would be achieving a couple of things.
After Tuchanka and Rannoch, the player could feel that things were going rather well. This delusion is brutally dispelled and the player is reminded of just who is winning here.
Bioware wants people to buy into the Crucible being the key to victory. With this raw demonstration of the Reapers' might, the player would be shown (not told!) the futility of conventional military resistance. The concept that Prothean device is our only hope would be reinforced.
This is supposed to be an apocalyptic conflict. Events creating a feeling of desperation and hopelessness is appropriate.
Finally we would be bringing the conflict to a head. We've seen our fleets and armies fail, the Reapers are on the march everywhere, and we one last chance to survive. A chance that Cerberus just stole from us.