This is insultig for the Mann brothers, they were much smarter and had more integrity than either Trump or Biden at the time they got their inmortality machines made, and they were old and needed inmortality machines at the age of 68.
Besides, gravel has it's uses, you need it for asphalt which was in high demand in the 50's and 60's.

Gravel also has its uses making Graveline! You know, the stuff that cars run on!