The article says part of the problem is vineyards. Those have a bunch of non-wood products (like wire) embedded in the vines which make it a costly, manual proc

The article says part of the problem is vineyards. Those have a bunch of non-wood products (like wire) embedded in the vines which make it a costly, manual process to disentangle the potential mulch from stuff that would either destroy the mulching machine or embed metal bits in the mulch itself.