The content linked from the article is unfortunately rather short on information but the video is well worth watching it.

Why are strings pulled with a particular force instead of just taut enough to wind wires around them? Does the inner string stay taut/"pre-stressed" because of the windings? I mostly wonder what warranted the effort to create a machine to wind strings by oneself though. A business selling bespoke strings, maybe?

I'd guess the motivation was to experiment with different string constructions, given the string shown in the video. Gut core is not common these days, and I don't think I've ever seen a wound string with alternate windings in different materials.