They're still there for, well, I can think of three reasons.
People vote for them. Organizing people to vote is hard for various reasons, but that mechanism is still present.
They're not murdered. Always an option, but certainly an escalation that doesn't scale well.
They're not expelled. Wikipedia says "In the entire history of the United States Congress, 21 members have been expelled: 15 from the Senate and six from the House of Representatives. Of these 21 members, 17 were expelled for supporting the Confederate States in 1861 and 1862. ", so that's not a commonly used option.
Personally I worry that if non-violent options fail, more people will see violence as an acceptable option.
Something like half of the US can't read at a 6th grade level. They cannot read and understand the complex writing at the bottom.