Why isn't Shopify collecting sales tax from out of state customers?

[NCSoda]

We are a business in GA, selling to both GA customers and customers in other states.  I have "collect tax" selected on all our products, but Shopify is only collecting taxes from GA customers, not out of state customers.  However, the state of GA says I am responsible for paying the sales tax on customers buying from other states.  If Shopify is not collecting it, why do I have to pay that sales tax, plus an income tax at the end of the year on that same revenue.  OR, is Shopify SUPPOSED to be collecting sales taxes but indeed are not?  Any one with some good insight on this, please help.  Thank you.  

[Ugurcan]

Generally, you are only required to collect taxes in states where you have a "nexus". However some states have additional rules. Shopify has a "Tax" plan you can activate, which automates such cases. 

See more here:
https://help.shopify.com/en/manual/taxes/shopify-tax