The reason why search engines are switching to LSI keywords is to avoid the spam keywords in the article
Let’s take a real time example.
If I need to optimize for a keyword “ what is SEO ” then usually the bloggers will repeat the same keyword over and over in the content and which looks spammy. Usually, they do this just to increase the keyword density and rank higher in the search engines. Doing this way is a very bad User experience because the content is written for the Google or for SEO and not for users. In order to avoid this kind of spam, Google has included LSI mechanism to show the results in the google search engine.
By using LSI keywords, you’re better able to create content that flows in a more conversational way. Using a specific keyword will generate results that are similar to the topic you’re discussing. This way you’re not overstuffing your content with the same keyword, making it almost unreadable by your audience.