3. Competitive Smash bans items and certain stages and stuff whereas the SF community likes to play games out of the box without having to set custom rules beforehand.
4. Smash is very unconventional compared to traditional 2D fighters. Instead of a lifebar and rounds Smash has precentages and stocks. Instead of blocking low or high Smash just has a shield, rolls, spotdodges, and airdodges. Instead of the same stage every time with a different background, Smash has stages that actually make a huge difference in how a match plays out. Even the terminology is different for the same concepts - Footsies and Spacing, Zoning and Camping.
5. Smash is made by Nintendo, a company with almost no experience making competitive games whatsoever. Capcom, Namco, Arcsys, SNK, and other fighting game companies have large teams of people working on the balance of their games and have NDAs with professional players. Because of all the effort they put into it, SF, Tekken, GG, BB, KoF, etc. games are usually very well balanced. Sakurai reportedly balanced Brawl himself. Look how that turned out.