And why we use quality content on our sites?
You do not have to use quality content, some sites deliberately dumb down
so that users frustrated by not finding what they want (or appalled at just how
bad a site is) are so desperate to leave they will click on an advert.
Welcome to SitePoint.
Unfortunately, your question is too generic to merit its own thread. This area of SitePoint (Web Content, Photography, and Social Media) is full of discussions on what quality content is and how it benefits your website. Take the time to do a search and read up on it. Being new here, you might want to start by reading the announcment at the top of this forum and the !IMPORTANT community guidelines at the top of each forum so you know what is appropriate here and what is not. Then if you have a specific question, either ask it in the relevant discussion or post it in a new thread if there is no open thread already discussing your question.