Sneak Attack is the defining ability that makes the rogue class what it is. Because of this, when designing a video game, you DON'T want to make it into a passive, invisible mechanic that you have to consciously think about to remember it exists. That's just following basic game design.
I'm usually very much in favor for sticking closer to D&D rules, but in this case I can't fault Larian for doing it this way. It's a core facet of how this studio implements D&D abilities in video game form. The battlemaster selects their maneuvers as special attacks, the rogue selects their sneak attack the same way. In complex games like this, being consistent is good.
NWN for example had many selectable abilities but still kept sneak attack as a passive, same with the original Baldur's Gate games.
