From https://account.mojang.com/login, there is a link to register an account. From the link above, this can be accessed from the Register a New Mojang Studios account link.
This link take users to https://minecraft.net/en-us/store/minecraft/#register, which redirects to https://minecraft.net/en-us/#register. This is the homepage.
The correct link is https://checkout.minecraft.net/en-us/store/minecraft/#register. As you can see, the subdomain 'checkout' is necessary for this link to function properly.
A potential fix would be to automatically redirect users who stumble across https://minecraft.net/en-us/store/minecraft/#register to the checkout link.