SEO optimization is performed to get a better ranking for a website in the search engines, thus attracting more traffic. However, even after SEO optimization, the website may still not get the expected traffic. This may be due to the following reasons:

1. Competitive: If your industry is very competitive, then even if you optimize your website for SEO, it may still be difficult to rank high in search engine results because other websites are also trying to optimize for SEO.
2. Poor Keyword Choice: If you choose keywords that are too broad or too narrow, then your site may not rank well in search results. Great keywords should be relevant to your site's content and less competitive.
3. Poor quality of content on your website: the sole purpose of optimizing for search engines is to increase the rankings and traffic to your website anyway, but the quality of the content on your website is also important. If your website content is of low quality, then it will be difficult to maintain visitor interest and retention, even if you have optimized your website for SEO.
4. Search engines update their algorithms: Search engines update their algorithms frequently, which may affect your website's rankings. In this case, you may not be able to maintain your rankings even if you have optimized.
5. Website Technical Problems: If your website has technical problems such as slow speed, dead links, lack of responsive design, etc., then your website may be ranked lower by search engines or excluded from search results altogether.

To sum up, SEO optimization is not just about keyword selection and ranking, it also needs to take into account factors such as the quality of your website and technology. If your website has been optimized but still not getting the expected traffic, then you need to double check and fix the above issues.