It's one of the only currents that has read and follows the traditions of Marx/Engels/Lenin, and thus recognizes that the source of capitalism and its class relations, imperialism, exploitation, etc stem from generalized commodity production and puts emphasis on it, recognizes just how important internationalism is in taking down a global system and rejects the concept of AES ('actually existing socialism' so Stalinist and later USSR + all modern day 'socialist' states) as being fundamentally flawed, it's relatively unique position towards tactics such as activism/terrorism/popular fronts/trade unionism and how revolution would be achieved compared to other currents and so on.

There's many more reasons, but in short its because their positions and critiques are the most theoretically sound in my opinion.