Maybe because the country is blocked in a two-party systems? In other democratic countries, you do not have "the left" represented by one single entity. You instead have a multitude of political parties that can negotiate with each others to push for their political goals. That makes the political landscape dynamic, new parties are created, reorganized, disbanded all the time.

In the US, if you are generally more aligned with the democratic party but see some changes you disagree fundamentally with, you either suck it up or give up your ideals and switch to the complete opposite (republican party).