I searched tweets by advanced search but some accounts' tweets don't appear. Why?
There are multiple reasons why you may not see some tweets when searching. Some possible reasons include:
The user has a "protected" account
If someone sets their Twitter profile to be protected, only their followers can view their tweets.
You may only be viewing "Top" results
In the Twitter web app, by default a search will return the top results. Check the other categories (Latest, People, News, etc.) to see different -- and possibly more relevant -- results.
Alternatively, use a Twitter mobile app (iOS or Android) to have the option to view all results.
Low-quality results are hidden
Results that Twitter deems to be low quality may not be shown. To see these results, click the Show option next to "Search filters" and change Quality filter on to Quality filter off.