Actually the new ones are where the chimneys were at one time. They used to go all the way up and have a cap on them above the roof line. Now they are not needed due to builders installing gas log fireplaces that use the same vent pipes as a normal gas furnace. They only need to go up high enough to get the vent pipe in the attic where it can go through the roof on the back of the house.
OK, mystery is 50% solved in my mind - I'm going with big tub, load bearing wall. I cheated and looked at some pictures. But I'm reserving 50% for a 2nd fireplace (whether on the 1st or 2nd floor).
Thanks everyone for your guidance here. Had me stumped. I'm down to two good ideas.
The house in question has an enclosed chimney all the way from 1st floor all the way up on back of the house. The bump-out is a second floor feature so not likely a 2nd floor pipe handler or its own fire box.
I doubt many new houses in the $350K range have a second fireplace.
I looked at 34 real estate sales interior pictures of the particular house and do see a big tub against the bathroom's outside wall. Unfortunately there is a big window for the tub that sort of rules out the bump being there for the tub since the bump has no window.
There are more expensive houses on the same street that have a full brick wall on the side of the house but NO bump out, just a big flat wall. All those with non-brick siding do have the bump.
Probably just too expensive to have a brick structure hanging out in space. They probably have the same tub but more support underneath.
Look at the photos again. The gas log fireplace is usually in the Master Bedroom. The bathtub in the photos you posted is on a long exterior wall and not on just a small bump out. Note the water closet and the shower on the same wall. The wall in the bathtub photo is at least 12 feet long and not just a small bump out.
As for the price range not having 2 fireplaces I put up quite a few of them that did have the second in the master. It was either use the bump out or set the fireplace inside the bedroom space.