Forum:Why did they abandon the program ?

The Reapers... In every other cycle they, they stormed through the citadel relay, ceased the citadel and through it, the mass relay network, and then just mopped up the isolated and defenceless systems one by one...

Now in this cycle they couldn't come through the citadel relay, but clearly they had no trouble taking over the citadel when they wanted to, so Why didn't they go with their old program and cease the mass relay network ???

Of course from the gameplay perspective, this plot induced stupidity is absolutely essential. (if they had taken over the mass relays, they would have inevitably won and there would have been no Mass Effect 3) but is there any in-universe reason ?