It probably has to do with the floorplans you've been choosing to look at. If a TT has one slideout, it will almost always be street side, to not interfere with use of the "patio" space on the curb side. If there is a slideout, it will be occupied by a sofa or a dinette. If the dinette is large, that is what will be in the slide.
Most of the TTs I've been looking at have curbside dinettes, or front dinettes, but I've been looking at only models with no slideout. A couple of floorplans I've noticed most manufacturers still offer in lightweight or base level model lines:
About 21 foot, front walk-around queen, streetside kitchen, rear bath, curbside dinette midships.
About 24 foot, front queen walkaround or in corner with foot and side open, streetside kitchen, transverse sofa separating bedroom from living area, curbside dinette, rear bath.
When length drops to 18-19 feet or less, the dinette moves to front or back and often becomes the primary bed. Bath is at opposite end.
These floorplans have not disappeared, and most dealers in this area still have them, selling mostly to older couples looking for something lightweight to tow.