Because American democrats call themselves liberals, and it is inconceivable to them that they might share something in common with Republicans (gross)

When it's pointed out to them that property as a right is a central pillar of capital-l liberal while being the central point of contention in leftist ideology, they simply deny property is any issue at all to left wing ideology except at the fringe (gross)

In the war of rhetoric, people like to use terms to try and bias you to their side.

liberal actually just means "free" and so there are many types of liberalism: social liberalism economic liberalism (as in free market economics) political liberalism etc...

In the USA liberals tend to be highly socially liberal and highly political liberal. Social liberalism tends to be associated with the political left, and when using liberal as a pejorative, it's usually meant to claim that the opponent is "too socially liberal."

US liberals also tend to be associated with the creation and maintaing of a welfare state which is commonly seen as being a left wing concept.

In the US, there is also a large history of debate between what the size and scope of government should be, and how the government should be run. This debate can somewhat be characterized as "liberal democracy vs populism", i.e good governance based on institutions rules and ideas versus well, populism, a decent example is Donald Trumps rhetoric about "draining the swamp." US liberals tend to be associated with institutionalism and supposed "good governance", and populism is commonly seen more as a right wing ideal, so in this area US liberals are considered on the political left as well.

It seems to me that this is how the term is used (excessive capitalism) in a lot of non US places.