Not just the rules, the equipment/gear is also different. With Table Tennis, you can use pips-out, pips-in rubbers and various blades.
On the other hand, only Sandpaper paddles are used in Ping Pong. You can’t use these to compete in Table Tennis tournaments.
With Table Tennis, there’s a best of 7 games with 11 points in each (used to be 21 before). With Ping Pong, it’s 15 points per game.
It’s best of 3 in Ping Pong except for semifinals and finals where it’s 5.
Even with scoring in Table Tennis, you’ll need double points if the game goes to 11-11 (deuce). On the other hand, 15-14 is a winning score in Ping Pong.
Because of the nature of equipment used, there’s a lot of spin/speed and service combinations in TT. Because of this, it’s also more appealing to the audience.
With sandpaper paddles, it heavily limits what you can do. These use two laminated layers instead of the rubbers that Table Tennis paddles use.
For the same reason, Table Tennis paddles are a lot more expensive.