I think your confusion comes from the fact this wasn't a protest gone awry, it was an organized domestic terrorist attack. It was a small group of armed people in body armor who privately organized a domestic terrorist attack intending to cause damage and hurt/kill federal officers in an ambush. The only reason the officer lived was because Song's gun jammed before he could kill people and get away.

Certainly if this was a jihadist attack, a lifetime sentence would be appropriate. Why should it be different just because they're white?