There are some startups that make tools for lawyers. Non-lawyers probably aren't aware of them. FastCase seems like a fairly new company to me. Others mentioned Clio.

If the question meant, why aren't there startups replacing lawyers, possible answers include: 1) In the U.S., non-lawyers can't be owners or investors in law firms; 2) There isn't a lot of overlap between the tech industry and the legal industry; 3) Much substantive legal work is custom knowledge work that would require a human level AI to replace. An approximation won't work.

There is still plenty of money to be made with something that helps lawyers do their jobs. Suggest document assembly as ripe for disruption. Existing tools are too costly.