why web interfaces are limited in search capability

Webpages have content. For text content, a common task is to search for something.
Web browsers have a plain text search feature, usually mapped to ctrl+f.

Why don't websites feature richer search functionality? 
For example, sorting tables, regular expressions for text, SQL, Cypher/Gremlin, infinite scroll (rather than pagination).

Answers include

• adding complex functionality takes effort
• most users will be confused by advanced search capability
• complex search features can be used maliciously/incorrectly if direct access to the backend database is allowed: 
• a user could delete data via SQL
• a user could edit data
• if a user is given read-only access to the server, a user could write an infinite loop and saturate server resources

Shipping all the data to the front-end isn't reasonable when the data is large (e.g., more than 1 MB), so interaction with the back-end is necessary (e.g., for pagination).