Whereas the chance of this taking off and making them tons of money is pretty low I'd assume? And if it doesn't it could mean another studio closing down.
At first SD bombed, but then on PC and word of mouth it really picked up in sales and S-E was pretty adamant that they considered SD a successful series that they planned to continue with as one of their core titles. Just seems like the most sense would have been making an iterative sequel using the same engine, a lot of the same assets and creating a new city, new story, upgraded combat mechanics. Nobody needed them to change the face of gaming with SD2, it could've just been a "Let's take what we learned from SD and do SD but even better!"
Maybe they're still making a SD2 in secret while doing this, who knows. Would be a nice surprise.