That's so Joe Schmo doesn't sue the company across the street from drilling into an oil reserve that happens to extend under his property. You can't really extract underground resources while respecting above-ground property lines, especially when you're talking about liquids or gasses.
It's not like they can demolish your house and build a pump there just because you don't own what's under it.
When I found that I storing the water that falls on your property might be illegal I was flabbergasted.
Also all the subsoil mineral rights. A company might just demand to extract oil from your property.
These things change according to jurisdiction but they are not uncommon.