This is just a means of controlling the language. If you read any older political book, you will never hear the term, socially liberal and fiscally conservative. The left has been trying to control the narrative through language for years, the right has not yet figured this out, although we have been doing better in the last couple of years as conservatives have gained a presence on social media.
The often percieved 'social' and 'fiscal' side of politics are actually different sides of the same coin. I'll bet you have never met anyone who said they were socially conservative yet fiscally liberal. That is because it is an oxymoron. A socially conservative view would naturally lead one to be fiscally conservative. In the same way, a socially liberal view naturally leads one to be fiscally liberal. The proof is clear. You have never heard someone say that they are socially conservative and fiscally liberal! This is because liberals are not pushing that narrative. Liberals do not want to push that narrative because that would lead people to be conservative, not liberal.
The reason why socially liberal and fiscally conservative helps the liberals is because, if you are socially liberal, you must believe in the social programs that the left espouses, or, at the very least, calling yourself socially liberal lends itself to openness toward those types of things because the social wrongs that the liberals say are present in society can only be fixed, according to the liberal theory that socially liberal people are espousing, by government welfare.
Also, socially liberal and fiscally conservative ensnares some conservatives by making them feel good because they say they believe in what is percieved to be good about the liberal agenda while also saying that they agree with what is perceived to be good about the conservative agenda all the while escaping the perceived bad stuff from each. But the bad stuff cannot be avoided. You are either a liberal or a conservative. Calling yourself both does not change the fact that the 'social' side of politics drives the 'fiscal' side of politics.
Socially liberal and fiscally conservative is a wolf in sheep's clothing, claiming to be the best of both worlds while really leading one to advocate for liberal positions that ultimately drive fiscal issues to the liberal side.