The reason why Netflix cookies may stop working after a few days is because they are not a legitimate way of accessing Netflix content. Cookies are small files that store information about a user's login details and session information. When someone shares their Netflix cookies with others, they are essentially allowing them to access their Netflix account without actually sharing their login credentials.
However, Netflix actively works to detect and block the use of cookies to prevent unauthorized access to their platform. As a result, cookies may only work for a short period of time before they are detected and blocked by Netflix's security measures.
Additionally, it is not recommended to sell or purchase Netflix cookies as it is a violation of Netflix's terms of service. It is also important to note that adding extra profiles or email addresses to a Netflix account through the use of cookies is not a secure practice and can lead to compromised personal information.
It is always best to access Netflix content through legitimate means, such as purchasing a subscription or using an account that has been authorized by the account owner.