Absence of american left

Why doesn't america have leftists?
There is far right, center-leaning right, and no one else because LMAO bipartisanism.

First world countries usually have some balance, but USA is like an obese man whose manboobs and stomach keep pulling him forward, but he works as hard as he can to avoid getting a strong back to lift the failures he created through his hedonistic consumption of dead animals.

Why doesn't america have leftists?

It does now. There was communist supression in the entire 20th century.
https://en.wikipedia.org/wiki/Anti-communism
Left-wing organizations couldn't function with anti-communist sentiment and state policy targeting them, but with left-wing infiltrating Democratic party they legitimized themself as mainstream movement - socialism isn't seen as path to soviet union, but a fair resource distribution system. Its very appealing when Wall Street types hoard all the wealth and power, the level of inequality that drives left-wing power is not actually the key, its contrast betwen richest and poor being showcased by mass media driving the crowds to adopt socialist ideas as more fair and egalitarian alternative to capitalism.
They're not wrong, just that choosing the tools of political violence will create another reactionary wave of communism and Anti-SJW/Anti-egalitarian sentiment(manifested in alt-right today) which will sweep society with another Red Scare.

>>2
Democrats are barely centrist, if that.
As a whole, they still support massive corporations, consumptionism, military interventions that primarily benefit Israel.
As soon as any Democrat comes up with an idea more revolutionary than "maybe people who suffer an accident shouldn't be doomed to permanent debt", the lower life forms (from both parties) start whining about the socjus boogieman that somehow has more power than the (((2%))) despite no one meeting any of them in person.

>>3
The conservative Democrats and the modern Democratic party are fairly different beasts.
Consider the left-wing is a trend that they're adapting, that much of the revulsion to socialism is now confined to explicit right-wing positions.
Socialism in eyes of young democrats is something like Scandinavian social-democracy paradise, not GULAGs and show trials. That of course gives fuel to more radical Berniecrats and actual socialists who can now be accepted as "more radical Soc-Dem version" and young people don't hold the prejudice towards the radicals, they're driven by economic realities not in their favor so they see it as an escape hatch from the system, accelerating changes towards more egalitarian future.

What does "Social Democratic" actually means:
https://en.wikipedia.org/wiki/Russian_Social_Democratic_Labour_Party