If you boil down the entirety of Twitter into just a CRUD app that allows you to post 140 characters at a time, then yes, you can make that in a weekend.
Well, how about recommended posts / people to follow (ML)? Sponsored posts with a buy button (3rd part integration)? Growth and metrics (data analytics)? A software product is never just about pixels on the screen; and trivializing the engineering effort behind it is insulting to Twitter employees, some of whom are brilliant engineers I know.