Perhaps your browser settings have cookies blocked
Or you are going to a domain that doesn’t match your cookie or your location. MathWorks does an IP detection to figure out where you are located. If your location matches the sub domain you’re requesting, MathWorks won’t be prompting you to confirm your location. If it doesn’t match, MathWorks will prompt you to confirm the sub domain of your preference.
If your cookies are enabled and you use the same browser, you won’t be prompted if you go to the subdomain you selected.