The Sonnet is definitely high end, depending on build options (Copper and Brass give obviously better sound and heft) can get into "luxury" category. It's a beautiful object too, fit and finish is top notch (I have one of the early GB models, dunno if Mode kept that level of quality).
Zoom75 is more utilitarian, and reasonable given the price difference.
It's a bit like watches really, maybe not that extreme but if you get a Casio G-Shock you get a very useful and solid watch for little money, but some people will prefer a Grand Seiko, Omega or Rolex because they are beautiful and well made. I get the difference between these keyboards is not that huge (more like mid-range vs high-range) but you get the idea
Reason vs luxury...