OK. Here's the "why". That drain line is leaking. Also, the vent and tee are behind the wall behind the cabinets. So, I have to find the leak and fix it.
The plumbing in the left cabinet (12" cabinet to left of sink cabinet) has a vent line above and then makes its way into the basement toward the stack but it looks like there is a 45 to take it out from the wall and then two more 45's in the rim joist bay in the basement to get it going in the right direction to the stack. There is also an old sani-tee which picked up the upstairs laundry (now abandoned).
That line ended up being the reason for some flooding and mold I had in the basement. A fitting before the stack had cracked and it was fixed. However, the tee in the rim joist area also had a crack and it kept leaking. I replaced all the abs from the floor down barely getting a coupling in to the pipe left after cutting out the old piping. I don't think I got the top coupling glued on properly as another leak developed.
So, I want to plan options for how I'm going to fix this issue. I'm asking about rerouting the drain here but I was also thinking about boring out the wood around the drain pipe in order to get more room to properly attach a coupling. Just trying to plan a fix without making it more difficult.