The Tottenham midfielder skippered the Three Lions for the first time in the goalless draw against Germany last week Friday and seemingly did enough to again earn the honour at Wembley.
"It's good experience for him [Dier],” said Southgate.
"I think being the captain on the pitch is one element of being a captain and showing leadership the rest of the time we're in camp is another part.
"The on-field part might help to raise the level of your performance, the level of ownership and responsibility.
"The bigger picture is we want some of these young lads to feel the responsibility a bit more.
"Eric has good tactical understanding on the field."