mysql - Waiting for table level lock on a table
Perhaps the users table is type/storage engine MyISAM and the others are InnoDB or perhaps the other tables aren't subject to many INSERT, UPDATE, or DELETE queries (IIRC, locking isn't used for SELECT).

See also:


way to prevent queries from waiting for table level lock
https://stackoverflow.com/questions/6543624/what-is-waiting-for-table-level-lock
https://dev.mysql.com/doc/refman/5.0/en/table-locking.html