Nurbs stands for Non Uniform Rational B-spline. Metanurbs are calculated differently from nurbs.
Lw doesn't support them basically because of tradition. It's never had them and previous teams never decided they were useful for the cost of putting them in I guess. Maybe the new team will.
You do have access to splnes and can extrude etc these, which you could then metanurb, it's up to you
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