How are capital losses factored in? My net losses for investments in 2019 were much greater than 3k, yet my refund is less than 3k. Shouldn't it be at least 3k?

Your capital losses do not directly add to your refund. Capital losses reduce your taxable income.

Capital losses will first reduce any capital gains that you have. After your capital gains are reduced to zero, they can reduce your ordinary income up to $3,000, and then any remaining balance is carried over to the next year.  

If your taxable income is already zero or your refund is already maximized by other deductions or credits, it is possible that capital losses will not increase your refund at all.  

capital losses reduce your income 

they do not reduce your taxes directly; i.e. they are not a tax credit.