The principal reason is the complexity of integrating ever-changing legalities from all three branches of government across all jurisdictions – and it's not just the logistics; it's the very modality of interoperation with democratic institutions. Despite a modern push for efficiency in public administration, extant inefficiency is still deep and vast, and capital markets can hardly bear it (i.e. investment in development of the concept).

But don't discount a secondary complexity – that of the contextual analysis and pure judgment inherent to legal practice, for which the human mind has a mysteriously unsurpassed capacity.

i assume not actively pushed b/c most get paid by the hour and by "customization to needs"