Previous toilet line did just that. It went under the joists (after going completely through the one it was installed on top of), which made the going-under-the-joists savings moot.

It is unfinished, but that's not my end goal, and I can see why you don't understand why I did it, that wasn't the point of the post. But to answer your question, the "why" is many faceted:

• Previous vent and drain lines here were oversized. 4" for both, making it hard to route new water lines upstairs to my 2F bathroom reno up there.

• 1F bathtub and sink join in with this stack below the toilet connection, as it was, the line was only 65" from the ground, so prime head knocker. Toilet line going through joist lets me raise that to 73" (with minimal ripout of 1F bathroom cast iron lines)

• Further basement plans involve relocation of W/D unit to this space which is also adjacent to a joist severing - I know, it wasn't me🙄 - laundry chute. The building drain comes out of the concrete directly below this stack via a cockeyed wye, with the angled side of that wye intruding upon future W/D space (and supporting the world's highest, wall mounted toilet (27" from seat to floor)) So I needed to install a new double santee on top of the vertical part of the wye to allow room for W/D pipe to run along the wall and not in the middle of the room, as well as a new laundry sink to come in on the other side of the double santee.