Why do we get so upset when our candidate is not selected as POTUS?

I'm just here with the popcorn to watch the inevitable right vs left name calling and personal attacks.

It is the policy changes that bother me the most, all the progress that was made under the GOP was trashed by the left as soon as they got into office. The Southern Border Crisis with all those unaccompanied children, drugs pouring in, rapists, and criminals among them. The American people's safety, health, and welfare should be always first. I for one do not want my tax dollars supporting any type of immigration unless it is legal immigration. We all have our opinions just like we all have assholes, I prefer all be done legally in accordance with the US immigration policies.

Because we hate each other, if I disagree I am a racist, I am a racist because I am white, I am a baby killer because I am a Vietnam veteran, we as Americans, we voted for Obama because he was black not because he was good for our country, we voted for trump because we wanted a better way of life,then came Biden who I did not vote for an now we’re going down a hole our city’s are burning we are killing each other, our four fathers are turning over in their graves for we have become.

People riot when their sports team loses. Presidential elections are just another way of expressing my team won and yours lost. It's not really a surprise that this happens.

The claims that it was all a fraud and actually Trump won, now that was a surprise.

Because each side has demonized the other where winning equates to the survival of the nation in their minds. Here is a sort of interesting article that mentions this: https://fivethirtyeight.com/features/why-the-two-party-system-is-wrecking-american-democracy/

Because the right is convinced that the left is a bunch of soy drinking liberals who are trying to destroy the country, and the left is convinced that the right is a bunch of beer swilling rednecks that are trying to bring back segregation and install a theocracy and mandatory Klan rallies.
Our politics don't support cooperation, only partisan fighting. Our political parties have become sports teams, one vs the other.

It started happening when enough of the voting population made it known through their voting that they are fine with negative attacks from their side against the other side rather than wanting to hear the policies and programs to decide whether they want to vote based on that, because they don't want to have to think that hard.
And arguing and calling the other side names takes no effort compared to even an elementary understanding of economics.
I don't know how long it's been going on, but the earliest famous example I can come up with is the "Daisy" commercial.
in 1964, the incumbent was LBJ, and Goldwater ran on cutting social programs, aggressive military action and even using nukes where necessary (as opposed to using just nuclear deterrence).
The attack ad, ran on prime time Monday night 7 SEP 1964, started with a girl in a meadow counting petals on a daisy. As she reached 10, a male voiceover started a countdown to zero, that ended in slo-mo footage of a nuclear detonation. It only ran once, but it stayed in the news and the weekend news shows for weeks.

The irony is that LBJ was casting Goldwater as a warhawk who would escalate Vietnam and possibly use tactical nukes, and obviously cut social spending, while LBJ was running on a platform of pulling our troops out of Vietnam and letting the South handle it, in addition to the Great Society and the recent passage of the Civil Rights Act.
At a speech the following month, he stated" We are not about to send American boys 9 or 10,000 miles away from home to do what Asian boys ought to be doing for themselves."

While we can all agree that social spending is an every election issue, by 1964, Vietnam was a pretty big election issue.

Troop levels in Vietnam in 1964 were 23K, By 1968 they were at 536K, the highest of the entire conflict.

But by that point we had already well established with DC that we are fine with attack ads and little to no content, so we continue to get the gov't we deserve. Every generation has reached voting age with far too many having been taught only that one party is right and one party is wrong, with no explanation of why.
And they didn't even bother to ask. Or read for themselves.

Because they have no life. Otherwise they could and would move on. It happens every cycle.

It is all part of the game. The left and the right are in bed with each other to keep America at each others throats so we don't pay too much attention to our corrupt and power hungry politicians. Thier plan for getting and keeping power has worked beautifully for decades. There is NO accountability for the laws they break, there is no accountability for the people who are destroyed. The left have recently gotten the upper hand with the media and social media as well. The right have been slipping with their complacency over having all 3 sections of Government form 2016 to 2018. Now the left have it back. People just don't seem to see the truth and that is just as well. We are all slaves to this system of Government where ignorance is bliss. We go on about our lives living off the table scraps our Government gives us and we pretend we have any say in how things go. We don't and we never will. That is just the truth of things.

It's at the point where we need to split the country in three. Give the right a piece give the left a piece and give the moderates a piece. With all three groups given a piece of this country then we can see who governors or provides its people with best solutions. Let the left fight amongst themselves let the moderates slowly figure something out as they will need the most time. And let the right governor as they wish.