Because if the Coron designs, they will never be as cheap as a Creality or Anycubic, even if you buy all of the stuff from China. Also, I would bet that many people that build a Voron spend more on their hot end and extruder combination that it would cost to purchase an entire Ender 3. A genuine Bondtech LGX attached to a Slice Copperhead, for example, is not something you’d find included in a mass-produced, low cost kit printer.
I have always wondered about the Voron 0 though - all of the expensive parts that make a Voron cost what they cost are there, and the parts that the design cuts back on are the cheaper printer components. As they say in shipbuilding, steel is cheap and air is free, so if you can make it bigger, then make it bigger. I guess the smaller bed tightens tolerances on frame movement, belt length, etc. which could (in some circumstances) translate into better mechanical control and fewer print artefacts. For mine though, I’d eat the extra cost and go with a Voron 2.4, which probably represents better bang for buck in terms of print size, without compromising anything.