Summer signing Mathieu has been greatly impressed by the complex in Burton upon Trent, where he and his Barca team-mates have been working this week on a pre-season training camp.
Regular occupants England crashed out of the World Cup this summer at the group stage, managing just one point and two goals in their three pool fixtures in Brazil.
And France international Mathieu said on Friday: "I don't know why, having these lovely facilities, England haven't done well - it is something I cannot answer.
"The English team would be the right people to answer that question.
"We only can say that we have enjoyed so much the great facilities and the amazing pitch.
"All the team have been so happy to train together and to get to know each other much better."
The experience will have been particularly significant to Mathieu, with him having only just joined the Catalan outfit from Primera Division rivals Valencia.
There have been questions raised about the 20 million euro (£15.9million) fee Barca paid out for the 30-year-old.
And, as he looks to establish himself at a club who have lost the services of the retired Carles Puyol, it would appear Mathieu has a significant task on his hands to prove himself at the Nou Camp.
However, he insists it will be a "pleasure" trying to replace former skipper Puyol at the back and is feeling optimistic about his prospects with his new employers.
"To be honest, for me it is a pleasure to play in the place of Puyol," Mathieu said.
"Obviously everyone knows he was a great player, but for me, this is nothing impossible. I will try to do my best and hopefully I will do well for Barcelona."