Tunnel boring is a complex, multi-faceted civil engineering discipline with a large number of well-funded firms that are aggressively competing and innovating. In this space Elon is utterly insignificant.
The ELI5 version is: "Elon thinks he can dig tunnels faster and cheaper than anyone else, but so he's failed to demonstrate he can create even one useful tunnel. The only reason he's doing this is because he hates traffic and thinks that driving in a private tunnel will make it easier to get to work on time."