Surely you answered your own question!
They have a gigantic range of phones. They don't need to create a new one to rival the SE.
And anyway, these S8's are supposed to be the same size as the S7's - it's just the screens that will be different.
TBH I can see already that this S8 may be one to miss out on, and they will have refined it much more for the S9 or Note 8.
That fingerprint sensor placement looks silly, the camera is rumored to get only a modest improvement, similar battery (but for a bigger screen, don't forget), and it doesn't look like the speakers will be wildly better (but let's see).
The leaks have dampened my enthusiasm, but hopefully they have some tricks up their sleeve!