Larian don't understand the workings of the 5e rogue rules - you are not supposed to get an 'extra' bonus action (that is actually forbidden in 5e - you can google extensive rules discussion as well as references about this. It is not valid). A Rogue is simply meant to get an expanded list of things they can do with a bonus action at a later point, but of course, Larian have made this overpowered by ignoring the rules. I don't know if they simply don't care or if they think it is 'more fun'. Rogues can already sneak attack every round in base 5e (its very easy t get advantage in comabt) - they don't need additional help, unlike some core classes that do seem weak.
