When you customize your meta title and meta description for your 
website's pages, you might expect them to appear exactly as you intended
 in Google's search results. However, Google's algorithms have the final
 say in how this information is displayed, and sometimes, it might not 
match your personalized content. Several reasons contribute to this 
behavior, and understanding them can help you optimize your content for 
better search result presentation.
Possible Reasons
Technical Reasons
Solutions
Remember that while optimization helps, Google's algorithms have the final say. Focus on providing valuable content and adhering to SEO best practices to improve your site's overall performance.
For more information refer to the official Google website  Google Webmasters Support.