That's really odd, I wonder if it is something they just started doing?
An old friend of mine has a son that was a pilot in the Air Force. Many years ago his son was trying to ‘make’ the Thunderbirds. The Air Force was just changing over to the F-16 for the Thunderbirds. This was in the early 90’s. He said his son told him that the F-16 had such better maneuverability than the T-38s that they decided not to wear suits. He said that was what washed his son out of the program. He just could not take the sustained higher Gs without a suit.
Maybe the Air Force thought better of it and kept the suit.
The F-16 has a side stick controller with it's own dedicated arm rest. That makes it different from all previous Thunderbird airplanes flown by the demo teams up through the T-38, because they use a conventional joystick.
The Blue Angels narrator specifically says during their performance, because they have the conventional stick, that G suits do interfere with the precision necessary for their control inputs. It is entirely possible that the T Birds had the same approach before the F-16.
The F-16 is the first demo plane capable of pulling sustained 9 Gs while maneuvering. Most designs before that were in the 7 G range, the T-38 was an older design in the 6.5 G range.
The F-16 ejection seat reclines at 10 degrees more that other ejection seats. It is supposed to help the pilot pull more Gs longer, so the maneuvers used by the Thunderbirds are more extreme to take advantage of the design.