For many reasons, though here are a few. He was visibly emotional when LA was describing Jennifer as mom (pinching the bridge of his nose, cheeks flushed, nose was red). He spoke up about knowing a witness about to take the stand and he spoke to the judge honestly, precisely, and without fear or intimidation of what he wanted to share...he didn't want the acquaintance to be an issue later on. He leaned forward intently to watch videos being played. He rocked back and forth in his chair with arms crossed under his armpits when JS was argumentative toward a witness or long winded, which was often. He also did this a lot when the interrogation videos were being played. He looked at the State gallery at least 3 times that I saw during closing arguments (both sides). He took constant notes (and I believe was on his second notepad at closing arguments). I felt like he was all of us if we were jurors. Wanting to jump out of his chair at times, following intently, watching every move in the courtroom. I just took him as someone who was non-verbally speaking through this entire trial and may want to share perspective from his chair. It's just a guess and JMO.
That's not to say that other jurors won't speak, there are a few others I think may and I would be surprised if a few others did. I am not a jury expert, just someone observing the jurors from inside the courtroom weekly since the trial started and that's my take.
MOO