I have been having this same issue for the past week. With all these steps you guys have mentioned, the variations would still not show up. I figured out how to get them to work as they should.
With all the steps mentioned above, you MUST also have a “Price”. Once I did this, the product page has everything (variables, add to cart, etc) that is suppose to show.
Variations-Bulk Edit (dropdown)-prices
Then add your price for the product and Update the page, then refresh your product page, and Voila! Do not put a $ in the price, just 0.00 format. (NOTE: my prices are all set to $0.00 because our customers are not all on the same Volume or pricing.)