Standard contracts exist for a variety of reasons, time/cost being one of them. Another one I'd like to highlight is the principal-agent problem[0]. If, due to automation, contracts went up by orders of magnitude in complexity then clients would be exposed to a new set of risks with a legal basis that they do not understand. The question then is: are these new, inscrutable risks acceptable to a client? Perhaps not, unless they are already a very large business.

[0]. https://en.wikipedia.org/wiki/Principal%E2%80%93agent_proble...