Their rating him for his potential. Under the right manager he could be England's no.1 defender. With the EPL stacked with so many good managers, he has a good chance to work under one. Some people even argue that David Moyes, who is manager of Sunderland now(?), is a good manager. 
Some said that he has the potential to be the next rio ferdinand if he is given all the regular time for him to play and so far he is getting that on everton so if he wish to move to a club then he should be considering his spot in the main squad rather than being a bench warmer because it might be affecting his career