Because increasing minimum wage is popular politics but it doesn't really solve the issue, and that is even if policymakers are capable of coming together to agree on how to make a 'livable' minimum wage (a livable wage in rural midwest is not the same as NY or SF for example), and how to keep that wage at a livable level without having to go through the political quagmire we currently are going through every 10-20 years. It isn't even clear that the minimum wage should be livable in the first place, as that also has its own costs as capital is liquid enough to go elsewhere leading to a race to the bottom.

Policymakers have shaped the economic system in a way that suppresses the value of unskilled labor, and simply forcing the increase has serious costs which most people don't appreciate, costs that are harder to bear for some compared to others, for example huge multinationals are much better equipped to deal with said costs compared to smaller, independent businesses. The appeal to emotion regarding this is especially dangerous since it often ignores the reasons why the problem persists, and when the problem is as difficult as this is, there are many potential pitfalls when creating a solution (especially a popular one), which can lead to making things even worse than before. The road to hell is paved with good intentions after all.

I think it is a little disingenuous to characterize people who are critical of concepts like a livable minimum wage the way you have, wage insecurity is a serious and complex problem that wont be solved simply by controlling the price of labor.

Ian Shapiro has a lecture about wage insecurity in his power and politics course at Yale that discusses UBI, minimum wage and other alternatives which I think provides a decent, but brief overview of the issues faced regarding policies like this. Here is a link specifically to where he starts to discuss the idea of 15$ minimum wage.

https://youtu.be/bldeaDRWJYc?t=2443