Honestly, in many instances they are just more expensive to design, not necessarily to manufacture.
Here's a sketch of what we've discussed:
View attachment 385700
Blue frame, gold feet, gray stand-offs, red foot-bars. Here's a section through the tailstock foot-bar:
View attachment 385701
I drew it with just one of the standoffs (of four) adjustable; that one's the twist knob. (In reality, I'd probably make them all the same but just think about adjusting twist with one.) Then the three frame feet are responsible for leveling overall (one extra adjustment!). There is some interaction between them, and unfortunately the way to deal with that is to adjust in a certain sequence. Adjust twist and then overall level. When adjusting level, if you first adjust about z-axis (the two feet under the headstock end of the frame), then adjust about x-axis (the one foot at the tailstock end of the frame), it will minimize interactions.
Looking at this section makes me think it'd be worth skinning the inside of the frame too, in the upper section, to remove the frame's tendency to twist. As with some other ideas, this may be going well beyond what the lathe requires.
I'm sure there are ways to make this even easier, but this doesn't seem too bad in the current state. The foot-bars could be sections of rectangular tube, which would give you more stiffness for a given weight, but takes up more room and may cost more; it also has a tendency to crush if a bolt tightens through it unless you sleeve the hole. I'd go with solid bar, like 4" wide and 3/4" or 1" thick.
The chip pan will prevent you from accessing the screws that connect the foot-bars to the standoffs, countersunk into the foot-bars, so I guess I'd do those only moderately tight so that the adjustment standoff can still turn. Alternatively, one could thread the hole in the foot-bar and run a long bolt the full length of the standoff from underneath, tightening into threads in the foot bar. That leaves the head accessible notwithstanding the chip tray. Only the adjustable standoff would have to be like that. The other three could get bolts from the top, tight and with threadlocker.