Come on mate, that wasn't an easy job.
It was a poisoned chalice at United and everyone knew it. Everyone said before he even went there that the person who would succeed at United would be the person after the person who replaced Fergie. And that was basically how it was. Van Gaal, one of the best coaches in the history of the game, did better but didn't do a whole lot better than Moyes did. Mourinho and Solskjaer haven't fared much better either. Everyone knew Moyes had a big re-build job at United. Half the 1st team were in their 30's when he took over. It's not like he walked in to ready-made champions. There are far bigger problems at Manchester United that he had to contend with, beyond just the playing staff - and it's the same problems those subsequent managers have faced and haven't been able to overcome either.
Most United legends like Neville, Beckham, Law and even Ferguson were totally against sacking him and believed he deserved more time. He got 10 months in a very difficult job, to try and recycle and rebuild, it was never going to happen overnight.