"Vote blue no matter who" attitudes can be thanked for this. People have been scared into never taking a 3rd party seriously. The Republicans are unthinkably bad so it is too risky to split the vote on the left. The only option is the Democrats. Corporations simply migrated their lobbying efforts slightly further over to the left side of Congress during the Obama admin. With strategically placed Senators like Gilibrand for Wall Street and Manchin for the coal/energy industry the corporate oligarchy has pretty good control over things now, the actual political desires of the electorate be damned. Notice how the democrats are politically leading the war/defense efforts now as well, something that used to be a more conservative aim.