No, it's because it's bullshit whose transparent purpose is to stoke fears about Muslims. Sharia Law is effectively already precluded from being passed as it is wholly religious in nature and thereby spectacularly fails the Lemon Test and certainly violates the First Amendment of the Constitution.
Not to mince words here, the point of trying to ban Sharia Law is wholly propaganda. Partially it's fearmongering to create the impression that Muslims are the enemy at the gates and are on the verge of overturning our way of life and rule of law, thereby making it crucially important that we definitively act to limit their influence while we still can. The idea is less to ban Sharia Law (as there's no risk of it being put into effect), but more to use the implications of passing such a ban to shape public opinion of Muslims.
This brings us to the second part: it's virtue signalling that Muslims are an 'other' and unwelcome, hence specifying Sharia and Sharia alone instead instead of crafting a more general ban addressing the underlying issues. That might read something like, oh I don't know...maybe "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof"? For those unfamiliar, that's the Establishment Clause of the First Amendment of the Constitution, which makes it illegal both to make any laws that would push us towards a theocracy and to make any laws that discriminate against a given religion. Which brings us back full circle with the fact that such a ban is redundant and unnecessary.