Well it wasn’t as simple as that. He was highly rated, arguably missing a chance to win GP2 (although Hulkenberg was dominating by that point) and he was parachuted into a dog of a car, in a team once focused solely on Alonso but that was now embroiled in the “Crashgate” scandal and seemed to have no focus at all and were going nowhere. It is relatively rare that a driver gets a second chance in modern F1.
And it isn’t as simple as “they brought him right back”, he was only confirmed very late on last year as driver for this season.