It’s pretty common to have these machines buried in the tunnel after they done the digging.

These are usually custom made one off machines that don’t have much of a life span beyond each project.

That was on some level the whole point of the boring company Elon said it was crazy that these machines were discarded or sold for scrap.

That said since recovering them would be much easier than landing a rocket I don’t know if there is actually financial motivation to recover them.

When they are sold they are usually sold for their effective scrap weight (metal worth minus the cost of getting them offsite and breaking them down).