Edit:2

>we're calling it free will but I might as well call it brain chemistry under incompatiblist determinism

I think you just have two different ways of describing the same thing. One is an emergent descriptions compared to the other. e.g. You could say that humans could be described simply as physics, but higher emergent descriptions using biology are more useful.

Free will is just a higher emergent concept above brain chemistry. Different sides of the same coin

Orig:

>Why do we have to call it "free will"? except to say that this naming might be convenient.

Isn't literally every word/definition just "convenient" naming conventions?

Studies show that most people have compatibilist intuitions, and most professional philosophers are outright compatibilists.

Most lay people, professional philosophers and criminal justice systems, call it "free will".

So it seems like society just calls it "free will". I don't think "should" or "have to" really comes into play.

You don't "have to" call it free will, but it just makes sense to call it free will, since it lines up to what people really mean by the term.

Edit: Some more studies you might be interested in

People have incoherent ideas around free will, but when properly probed the majority have compatibilist intutions.

>https://casetext.com/case/united-states-v-moore-48/
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>In the past decade, a number of empirical researchers have suggested that laypeople have compatibilist intuitions… In one of the first studies, Nahmias et al. (2006) asked participants to imagine that, in the next century, humans build a supercomputer able to accurately predict future human behavior on the basis of the current state of the world. Participants were then asked to imagine that, in this future, an agent has robbed a bank, as the supercomputer had predicted before he was even born. In this case, 76% of participants answered that this agent acted of his own free will, and 83% answered that he was morally blameworthy. These results suggest that most participants have compatibilist intuitions, since most answered that this agent could act freely and be morally responsible, despite living in a deterministic universe.
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>https://philpapers.org/archive/ANDWCI-3.pdf

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>Our results highlight some inconsistencies of lay beliefs in the general public, by showing explicit agreement with libertarian concepts of free will (especially in the US) and simultaneously showing behavior that is more consistent with compatibilist theories. If participants behaved in a way that was consistent with their libertarian beliefs, we would have expected a negative relation between free will and determinism, but instead we saw a positive relation that is hard to reconcile with libertarian views
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>https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0221617
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>Then when it comes to philosophy professors most are outright compatibilists.
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>[https://survey2020.philpeople.org/survey/results/all)