People doing SEO often get stuck on one question: the page has clearly already been indexed, so why can't it be found when searching for related terms? To answer this, we first need to distinguish two things that are often conflated—indexing and ranking.
Indexing is admission, not a score
Indexing means the search engine has added the page to its database and knows it exists. This only earns it the right to compete. To be found in search, it still needs to rank high enough in round after round of subsequent judgments. So "the number of indexed pages increased" by itself does not mean SEO has improved; it only means the search engine has seen more of your site.
Ranking looks at a different set of things
After a page becomes a candidate, the search engine must judge whether it is actually suitable for a certain query. The dimensions involved include: whether the content truly answers the question, how accessible the page is and how well it loads, whether other websites link to it, and whether users stay after clicking through or immediately return. These judgments stack on one another, and if any one is clearly weak, it may keep the page from ranking high.
Why the number of indexed pages is easily mistaken for the goal
Because it is visible, comparable, and changes can be seen quickly. By contrast, factors such as content quality and user experience are hard to quantify, and feedback is slow. This easily leads to a situation: to increase indexing numbers, large numbers of low-value pages are generated. Even if these pages get indexed, they can hardly bring traffic and instead drag down the judged quality of the entire site.
A few metrics more worth paying attention to
Rather than staring at the total number of indexed pages, look at these groups: ranking changes for target keywords, actual traffic brought by pages, and how long visitors stay on the page and their click-away behavior. These data can reflect whether the page is really working. Indexing data should still be watched, but its role is to detect anomalies—for example, if a certain section has never been indexed, that indicates a technical or structural problem.
Don't reverse the order
A common practice is to solve indexing first, then optimize content. But a more reasonable order is: the content itself should have independent value, then use technical means to ensure it can be smoothly crawled and indexed. Doing it the other way around is equivalent to pushing a batch of mediocre pages to the search engine first, and afterward it is very hard to restore its impression.
Indexing is the threshold, ranking is the result, and whether users stay is the final answer. Put your attention on the last thing, and the first two often improve along with it.