This is why. Well, this is one of the reasons.

First, we have extremely few liberals in America. The Democratic party is mostly made up of people that would be best described as center-right anywhere else in the world. They don't actually want to fight to roll back changes that Republicans make, and actually try to internally sabotage the few members that do want to undo changes the republicans make. They actively prevent change, and then active work against those who do want change all while professing to want change and to do their best to fight for it. But they're lying, and people are catching on. People are even starting to realize that the whole "We'd do stuff for you if it wasn't for that bad bad manchin, and Sinema" thing is as much of a lie, too.

The second reason that is more for the communists is something along the lines of the old joke "Scratch a liberal, and a fascist bleeds" Communists don't like liberals (And the use of the word liberal is pretty different from the usage in the first case) because they view them as people that profess to want these better for others, until it requires any, even minor, amounts of sacrifice from the liberal. The whole Moderate Rebels thing in Syria? It was always a lie for one simple reason. Fighting is an extreme action. Moderates don't fight, they just don't. That's one of the reasons they're moderates. Liberals are like communists that aren't willing to fight or do what is necessary to enact change.

In the United States, we refer to anyone in the Democratic party as "liberals". Many people refer to Bernie Sanders as "liberal". It's kinda dumb, but easy to get caught in when you live in it.